[Android Head-Units] pfdeadpool:
So after looking at head units for the last week or so I'll share some things I found useful:

Retailers: Aliexpress & ebay have been the 2 most successful for me, then Amazon (in that order) as far as selection, and typically price as well. Some misses for me were: dealextreme, alibaba, sonicelectronix, globalsources. Worse yet (hardly any hits): banggood, manutacturers, globalmarket, everbuying, miniinthebox, tomtop. You may as well try them all once you've decided on a particular unit, the first three will help you identify trends fairly easily though.

Searching:

Search terms: Android (4.2, 4.2.2, 4.4, 4.4.4) (quad, dual) (rk3066, rk3088, rk3188) (dual, double, 2 din) (1024, 1024*600, 1024x600) (800, 800*480, 800x480) (capacitive).......... you may want to exclude: win ce, wince, resistive, resistance, 800*480, dual core, rk3066, rk3088, dvd, etc.; depending on what you're looking for.

Keep in mind to check various categories (ex. eBay has many listings in both 'consumer electronics' and 'ebay motors')

Sorting aliexpress results by '# of orders' helps identify popular models

Keep in mind many of these head unit models have more than one variation (changes in CPU, RAM, screen resolution, OS, packaged accessories, etc.) so reading descriptions might help explain why one is $200 and the other clone $350

There's a huge variation in price of identical units. Shop around before ordering.

Some models are very popular in other countries (based on their reviews on aliexpress)

Some models are old(er) like 2013+ I think, hard to say.

Some units are advertised for a particular car. In some cases, the head unit is specifically shaped to fit in a unique dashboard. In other cases, the head unit may come with specific adapters for the car (like a CAN adapter). Other times, the head unit may in fact simply be a generic double din, with a search term attached to it in order to draw views.

I've identified ~8 models that pop up about everywhere I search. I'd like to hear more about them, if anyone can expand:

Newsmy:

NU3001 aka: CarPad, Car Pad, CarPad2, CarPad2s.

Identifying features: smooth, glossy screen. Unique styling of volume +/- buttons in lower left corner. No DVD optical drive.

Cheapest seen advertised shipped to US: $315 (advertised as having a quad core, 1gb, 1024*600); cheapest 2gb version seen $323.

^I do not know if this can be found with a dual core, or 800*480 screen. I don't think I came across any. Sometimes this is referred to as a CarPad2 (CarPad2 is also what the next model, the NU5002, is often referred to as)

NU5002, aka CarPad2, Car Pad2, 8" universal Android

Identifying features: Typically the same photo is used for these listings (the large, orange, home screen). Large glossy screen, no buttons. Very minimalistic, few features to identify. No DVD optical drive.

Cheapest seen advertised shipped to US: $425. As far as I know, there are not more than 1 iteration of this offered. Correct me if I am wrong.

CarJoying RK3188 RK3066 (possibly related to Joying/CarJoying. Often the numbers "2114" are in part of the advertised model name). If you have any good info about a model number(s) etc. please share. I just refer to it as "*that* one with the left center knob", or "Joying 2114". XDA link.

Identifying features: Round physical knob on left center of screen. Left column of buttons top-to-bottom typically is: Home, Back, GPS/NAVI, (Knob), SD/GPS slot (or, GPS/USB). No DVD optical drive.

^*note- there are many units out there with left-centered knobs, I am not referring to those, they seem to be a minority.

Many variations of this unit exist. Dual core RK3066 (rarely seen), quad core RK3188, 800*480, 1024*600.

Honestly I don't know much about this unit. It is very popular. It looks pretty nice from what I've seen.

Cheapest seen advertised shipped to US: $225 (Quad core, 800*480). $256 (Quad Core, 1026*600)

Possibly HuiFei, often listed as a HotAudio 2100". Also listed on CarJoying website

Identifying features: smooth & glossy screen, has a slot (believe SD?) in lower left corner of screen. Looks similar to NewsMy except the left column of buttons is slightly different; the volume +/- are differently styled between the two. No DVD optical drive.

This is another popular unit. There seem to be quite a few iterations available.

Cheapest seen advertised shipped to US: $215 (dual core, 800*480), $225 (dual core, 1024*600), $255 (quad core, 1024*600)

Possibly Ownice C200, aka Winlink. Also listed under CarJoying website, and Pumpkin website.

XDA link

Also seen in the Ouku unbranded thread

Identifying features: Two silver knobs in lower left & lower right corners. Two columns of buttons on left & right sides. DVD optical drive with buttons on left/right of it. *Note*: there are two other similar clones; one has the silver knobs in the middle of the sides, the second has the knobs at the top corners. I assume these are all structurally the same(??)

Cheapest seen advertised shipped to the US: $135 (dual core? a11/a9 833mhz? last gen processor?, 800*480, win ce?), $266 (dual core RK3066, 800*480, android 4.4.4), $279 (quad core RK3188, 800*480, Android 4.4.4). I've seen 1024*600 advertised on the unit with the knobs in the top corners.

*Note*- There are many things to be aware of before buying this style unit. It is very popular, but keep the following in mind when looking at them: Many apparently run Windows CE, "Windows 8" (New Win CE), Android, Android 4.4.4, or any combination of anything you could imagine (dual OSes). Many descriptions/listings are vague, and unclear about specifications. On aliexpress, this unit seems to be popular in Russia(?), not sure about that. I believe that it is an older unit which has been around awhile and seen many refreshes. That said, it can be found cheap, and many video reviews seem happy/positive. I don't know enough to give my own opinion. I do realize however, that my ignorance will lead me to choosing a different head unit.

Joying J-UQ121, J-UQ126, J-NQ122-2, J-TQ128.... and the list goes on. I believe this is manufactured by Joying; again, does anyone know whether Joying is a reseller only, or a producer/reseller?

[IMG="Model w/ DVD drive pictured"]http://www.carjoying.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/e/u/eu_warehouse_android_quad_core_head_unit_gps_navigation_system.png[/IMG]

Identifying features: initially looks very similar to NewsMy/HotAudio units. Glossy screen, almost no buttons. However, this unit has: a "micro map card" slot in top left corner, microSD slot in top right corner, two unknown buttons(?) on left side, and SOME have a DVD optical drive in top center (which sometimes is hard to see in pictures), some do not have the DVD optical drive slot.

Cheapest seen advertised shipped to the US: $224 (Quad core RK3188, 800*480, no DVD, $270 (Quad core RK3188, 800*480, yes DVD), $352 (quad core, 1024*600, yes DVD)

^These are basically the most popular models I saw continually on every site. They are also the ones with the most reviews, etc. I assume any would be an acceptable choice, given the right configuration.

Honorable mentions that I'd like to know more about:

Pumpkin Unknown model @$250 quad core, 1024*600

[IMG="Can be found on eBay, aliexpress, Amazon, Pumpkin"]http://g02.a.alicdn.com/kf/HTB1qX2KJpXXXXcEXpXXq6xXFXXX9/Pumpkin-2-Din-Flat-Panel-1024-600-Car-Stereo-Audio-Quad-Core-Android-4-4-Suitable.jpg[/IMG]

Pumpkin Unknown model ~$320 dual core 800*480, ~$350 quad core 800*480. Claimed boot up speed 12-15 seconds (could be warm boot, or simply inaccurate).

[IMG="Can be found on Amazon, Pumpkin, eBay, & I think aliexpress"]http://ecx.images-amazon.com/images/I/71PJEF8AdTL._SL1500_.jpg[/IMG]

Whatever this thing is; @$240 dual core, android 4.4., 800*480; ~$280 quad core

^all of these are fairly popular, but very hard to research for me.

Last subjects of discussion:

PPI. Can someone more knowledgeable than me please explain real world differences between using a 800*480 7" screen with ~133PPI, a 1024*600 7" screen with ~170PPI, and my 2560*1440 27" IPS monitor with ~109PPI?? (Not to mention my 2560*1440 5.5" phone with ~534PPI......). I'm wondering if/what is the reason to upgrade between 800*480 & 1024*600. I'm aware of the cutoff in perception of pixel density; I'm not familiar with how a capacitive touchscreen functions differently at different resolutions.

Processing power. Is there a real world difference between dual core RK3088 & quad core RK3188? I tried searching for anecdotes, videos, etc. -not much luck. I think I've seen both RK3066 & RK3088 in listings, not sure about that either.

Android versions: In my research, it seems that 4.2 was quicker than 4.4? I don't know much about versions of Android, etc. Any info? A lot of the discussion/debate was like today's Lollipop discussion: new is inherently bad, or focus on 1 or 2 particular aspects to make a particular version the "decisive" champion. All I really care about in a head unit is responsiveness, reliability/crashing, functionality with my phone/apps etc., and boot up time (honestly I don't think 25 seconds vs 35 seconds would be a big deal for me; 10s vs 40s might, don't think I've seen anything advertised as under 20-30s).

Personal notes: At this point I'm leaning towards a NewsMy 8" NU5002. Mainly because of size, manufacturer/community support, and aesthetics. I think the left-center knob model 2114 would also be good, and most likely the last CarJoying one as well (with the top map & microSD slots, & with/without the DVD drive). I'd really like to know more about those Pumpkin ones I listed at the end though, they look pretty nice. I would not go with the two-knobbed model; it is very popular, but IMO, I feel like buying a Chinese Android head unit is a big enough task in itself; I'd prefer to go with something more current/supported/easier to understand specs about. I don't really think I have run across anything worth buying that I have not posted, aside from a small selection of units with a row of buttons at the bottom of the screen. Some feature what appear to be tilting screens, which would be nice, but I am not brave enough to risk an additional thing going wrong (ignorance speaking), and I'd rather buy something popular in a situation like this. I'm torn between saving ~$200 between the NU5002 and the other runners- I'll have to modify the dash a lot (1.5 din Crown Vic), but my Note 2 taught my some very valuable lessons about screen size. I like the flat, glossy, screens; however, I can see how a physical volume knob could be described as a necessity.

NewsMy, CarJoying/Joying/Joyous, & Pumpkin, all seem pretty legit. Read reviews. Some positive reviews are one lines, no text, foreign, etc. Some negative reviews are for straight up user stupidity, not knowing what they were getting into, product not matching their car, etc. Sometimes you get helpful info like bugs/glitches, reliability over time, good/bad sellers, etc. You know the drill. Just a pain in the butt to go through it all, that's why I made the thread;)

***as always, mods you are welcome to edit this post for correction, clarification, etc. Please annotate if editing.