[Verizon Samsung Galaxy S 4] joshm.1219:
It's two Krait 300 cores, not 400. It's the MSM8960Pro, the dual-core version of the S4 Pro, prior generation to the Snapdragon 4/6/800 series. The funny thing about that processor to me is that they call it "X8" for the number of cores, but really what they define as a core is questionable. In their context, it really should be called the X11, and a modern Nvidia processor in the same sense would have over 80 "cores" lol.

That's not to say it isn't great and suitable hardware for almost anything. Like I said, in my own situation, I use my phone for things that really tax the processor. And it is technically going backwards in processing power, no matter how you cut it. Of course the software makes up for a lot of it, 99% Google AOSP. TouchWiz will always lag a little bit no matter what it runs on, I think.

Anyway, [MENTION=5493962]scryan[/MENTION], if you're looking to stay around the same generation or newer, on verizon flagships with unlocked bootloaders, you're options are limited. Of course, it's up to you how much you want to spend. Depending on your S4, in solid condition, you'll probably get around ~$250-300. You said you want a new phone in the $500 range, that will keep you in the same generation of phones pretty much. So you can pick from the LG G2 ($500 from Verizon, every retail OTA has root & custom recovery), the Moto X Dev Ed ($450 from Motorola, newest retail OTA doesn't have root so have to go dev), the HTC One M7 ($500 from Verizon, if on the newest OTA, it will cost you another $25 to unlock the bootloader).

The LG G2 is a comparable but not better phone to the S4 in my opinion. Super thin bezels, arguably easier to hold than the S4, with a slightly bigger screen. Same processor, but you can get kernels and AOSP on the G2, so a lot better than a safestrapped S4. Screen isn't really as good, I think. I prefer AMOLED over LCD. Camera isn't as good either. Regardless, it's better than the Moto X or the M7's. 3000mah battery is nice, not removable though so that's a downgrade for me personally. It has 32gb of internal memory, but no SD slot, once again a downgrade for me personally. The rear controls were easy for me to get use to, the knock code didn't really work all the time when I had it, don't know if XDA has improved that situation. Also, the plastic back feels even worse than the S4's and gets fingerprints even easier.

The Moto X, when were talking about it in the situation of power users, doesn't hold up in my opinion. I think comparing a stock Moto X to a stock S4 changes things. If you don't have to worry about the unlocked bootloader, you can get a customized retail version which is really pretty sweet. Plus, AOSP just flies compared to TW. The phone has a smaller battery but better battery life because of the software. Also, you could consider the Droid Maxx, which has a 3500mah battery and crazy battery life. I think I would get that if I had to, but the Moto X feels a lot better in hand. I think 720p is more noticeable on the 5" screen of the Maxx, and the hard buttons on the bottom of the screen are ugly. If you're only willing to buy a new phone that's bootloader can be unlocked, then you're limited to the Moto X Dev Edition. The Droid Maxx Dev Edition is no longer for sale new from Motorola or Verizon from what I see. The newest 4.4.4 OTA on the retail Moto X and Droid Maxx still doesn't have root, although I don't know what will change from all of that with the revelations from Dan Rosenberg and his TrustZone exploit, and his on-stage unlocking of a Moto X bootloader. Comparing them for me, a lot of the phone is a downgrade though. Camera is okay but nowhere near S4 in my opinion and many others. Processor, already went over that, although I must reinstate, the software makes up a lot for the disadvantages in the perfomance department. Screen is 720p, resolution downgrade although admittedly not as noticeable on the 4.7" screen compared to 5" screen of the Ultra or Maxx, where I can't justify 720p to myself anymore. Still like S4's screen more. Moto X fits great in the hand, better than any other phone, the polycarbonate is better than Sammy's plastic. The battery is better than a stock S4's, even if it's smaller. Although, it's not removable so downgrade to me. No IR blaster either or SD card slot either, although the Dev Ed is 32gb.

The One M7 is still a great phone and best alternative to the S4 in my opinion. It's root/recovery/S-OFF situation is weird though. For the newest retail OTA, the only method to temproot/S-OFF (to eventually gain permanent root and custom recovery) is Sunshine, which costs $25 to use. Same processor as S4, once again custom software will make it run better than a safestrapped S4. Way better build quality, way better speakers. Although, for me, I would still go S4. The camera is only 4MP, and the larger light aperture simply doesn't make up for that lack of resolution in sharpness compared to pretty much every flagship camera these days. Battery is slightly smaller, but once again nonremovable. 32gb internal memory, but once again no SD card. I think the build quality really makes up for a lot of that though. It feels way better than every other Android phone except the M8 lol.

So, to sum up, if you're looking for a new Verizon phone in the ~$500 range that's bootloader can be unlocked, you can choose between the G2, One M7, and Moto X. Out of these, I believe the best alternative to the S4 is the One M7. I would probably take the G2 over the S4 if I didn't care about removable battery/sd card, because I value that more than AOSP and custom kernels.

Personally though, I use Swappa and haven't had any problems using great condition used phones like the S4 you want to sell. If you consider options on Swappa, you can get a better phone than these or get a far better deal on these phones. Or even get an MDK S4 lol.