[T-Mobile Sidekick 4G] jsyi84:
Since I have all three phones in question I'll add my 2 cents...

Battery life: G2 - SK4G - MT4GS

I talk on my phone about 2.5 hrs, play games for about 30 mins, check my daily news/forums for about 30-45 mins, and listen to Pandora or Winamp for about 6 hrs per day. On the G2 I was golden all day and had plenty left to get me through up to the middle of the next day if I forgot to charge it that night..... Not so with the SK4G or Slide.... SK4G might last me 8-9 hours whereas the MT4GS has last me as little as 4 hrs and up to the max of 11 hours(8 of which I was sleeping....). Therefore I ALWAYS carry with me a total of 4 batteries at any given time with my MT4GS or I won't get through the day.....

Multitasking: G2/MT4GS(tie) - SK4G(extremely far behind)

I agree with Tsloble. It has to be the ram....

Camera: MT4GS/G2 - SK4G

Although the MT4GS has an 8mp camera whereas the G2 is 5, you probably won't notice much of a difference between the two. Considering I shoot $3k+ full frame DSLR's a camera phone picture is always just that....a camera phone pic. On the other hand the SK4G camera is mediocre at best....you'll easily pick the SK4G photo out of a lineup...

Flash: G2(leaps and bounds better) - MT4GS(standard) - SK4G(uh...)

Yep...that mighty G2 has a true death ray flash...no, seriously... I doubt you could ever come across a brighter phone flash... The MT4GS' won't impress... and the SK4G......leaves much to be desired(think blueballs..HOW HARD IS IT TO PUT A FREAKIN LITTLE 2 CENT LED NEXT TO THE FREAKIN CAMERA?)

Keyboard: SK4G - MT4GS/G2

SK4G definitely impresses as it's the closest to a real keyboard you'll find without getting on your computer(ooh the wonderful number key row)... The MT4GS/G2 keyboards both have squishy button feel(not the good kind) and offer no real feedback..

Keyboard/screen hinge mechanisms: SK4G - MT4GS - G2(a definite POS...)

The SK4G screen slides up so buttery smooth it almost feels like it's hydraulic(think of the hydraulic struts that hold up the backdoor/liftgate of a minivan or suv) whereas the MT4GS feels more like when you open the hood of a truck or suv that has those coiled spring hinges that make a creaking/squeaking sound as you lift it up but offer some assistance. On the other hand, opening up/closing a G2 keyboard feels more like when you slam the trunk or hood of your car closed....you're almost afraid to slam it shut too hard in fear of breaking something.... lol

Speaker quality/position: MT4GS/G2/SK4G(all are equal)

The position of them all sort of suck in one way or another....at least for my fat fingers and the way I hold my phones. 75% of the time I find myself covering the speaker grille while holding it to play games or texting which prevents me from hearing my music or sound effects... Gets annoying sometimes but nonetheless they all do their job at providing mediocre at best tones without any speaker crackling, aluminum foil wrinkling sounds. Good thing we don't buy phones based on their speakerphone....

TV-OUT: MT4GS - SK4G - Obviously the G2 isn't a contender....

As mentioned before by someone else the SK4G doesn't fill the whole screen whereas I haven't had that problem with my MT4GS. **** looks just fine on the MT4GS

Android/Hard-Button placement: G2/MT4GS - SK4G

The G2 and MT4GS hard-button placement is similar as are pretty much most HTC phones although the MT4GS(as did the MT4G) has additional hard keys over the G2 due to the G2 home/back/search/menu keys being capacitive touch...very easy on the hands. With the jump key, home, back, menu keys being on opposing corners of the phone, the SK4G has some screwed up button placement as do most Samsung phones(vibrant, galaxy s 4g) which makes for an awkward one handed experience that will take some(lots) of getting used to if you weren't a previous SK user...

OVERALL:

Without getting into the modded/rooted ability of each phone if I had to do it all over again and only got to choose one phone and keep it stock it would be the G2 due to the absolutely freakin' amazing battery life, compact size, awesome flash and speed(yes, I feel it's fast stock). The lack of FFC doesn't bother me since I have NEVER taken a single photo or used video chat with my MT4G, MT4GS, SK4G or Galaxy S 4G....

On the other hand we are in the last quarter of 2011 and not last quarter 2010 so I don't see a point in getting a G2 anymore as I feel game/app development will move ahead beyond the abilities of what the G2 or SK4G will be able to handle and there will be a time when the bare minimum will be a dual core processor/better gpu to play a graphics intensive game that will even be a challenge for the MT4GS. You wouldn't want to play Team Fortress 2 or Counter Strike on a Pentium 4 machine with integrated graphics.... as I myself prefer playing at bare minimum an i5 machine with an nvidia gtx 460.... The keyboard is something you can adapt to and over time becomes a nonissue as are things like button placement and aesthetics. However, the important thing is the actual brains/guts of the machine. You can't add ram, change processors or gpu's of our phones as you would a computer...

In closing the G2 was then.....the MT4GS is now.