[Galaxy S 4 Q&A, Help & Troubleshooting] BigJim.T32:
Just a little feedback on Official Cm12.1 (CM 12.1 build 2015/11/17) - been using this as a daily driver for a few weeks now (using novalauncher for my homescreen).

Performance & battery has been generally fine - even with moderate use (wifi or mobile data constantly left enabled, plenty of screen-on time, lots of photos, frequent use of whatsapp & SMS, email etc - but not really anything particularly draining such as long trips with GPS, or extended media usage), I get a good 2 and a bit days from each charge...

I'm sure I'd find my battery taking more of a hit if I were using it as an MP3 player to/from work, or having to use GPS frequently, but for day-to-day usage, battery has been excellent.

The included camera is good - nothing special to report (which is a good thing imo). No bugs, no unexpected behavior for good or ill, and no need to change the camera app unless there's a specific need (for higher-end functions, etc..).

Nightclub, low-light photos have been acceptable, daytime "optimal circumstances" pics have been great.

My girlfriend's S5 (using Samsung-branded rom) camera is more annoying, taking longer to find focus, is more temperamental (sometimes will only find focus if flash is on) and more unpredictable in what the resulting image will look like.

I'm not a camera geek (unless we're talking film SLRs), but I prefer mine to hers.

I've tested the GPS a few times, from cold-start it's about as quick as my standalone tomtom unit (not enough difference for me to put them side by side to test), and definitely faster to locate my initial position than my Gal-S2 using stock rom.

No drop-outs yet, but I've only used it briefly for testing, I've not had to do any long distance trips yet.

Again, only my gut feeling, but if it had taken an inordinately long time to locate me, then I'd have done some further testing...

Stability has been wonderful - no reboots, no mysterious crashes, or hangs to date.

I did get an error when I first installed, because after flashing the rom I (foolishly) rebooted before flashing GAPPS (which I should have done *immediately* after flashing the rom before leaving recovery), but a quick factory wipe & reflash of GAPPS sorted this without even having to reflash the rom. Bonus.

The only annoying things I've found are;

A) Lack of USB mass-storage (UMS). This is intrinsic to android though, only going back to version (what? 4.2? 4.4? Something like that) would help as my understanding is that it is simply no longer supported as a whole, and not the fault of any specific rom.

There is a semi-hidden option to use UMS available when the device is already connected to your PC via cable, but so far this has been of little use as it still doesn't let me access the SD card like the old Mass Storage function used to.

B) USB OTG. Worked out of the box first time, but after that first use, my device no longer detected a USB OTG cable was connected.

To rectify this issue, I simply rooted the device, and used Chainfire's StickMount (or USB OTG helper, either app worked), and now USB OTG is again fully supported.

I can't give any constructive feedback on the other roms you suggested - I briefly tried Official CM13, but one of my "must have" apps (ACR - automatic call recorder) was not playing nicely with CM13, so I immediately switched to CM12.1, and the exact-same .apk now works flawlessly.

I can't say if it's to do with Marshmallow, the CM13 rom, or what, so that's only a tenuous, anecdotal report.

Anyway, hope this helps narrow it down for you - for me, CM12.1 has been perfect; Stable, good battery life, and no unexpected behavior - pretty much everything I want from a rom tbh...