Here’s an updated list of compatible ROMS for the U.S. version of the Samsung Galaxy S2 (SII) or the Samsung SGH-i777. These are all confirmed roms that are running and stable for our phones; exception is MIUI but it’s on the list. Don’t go flashing ROMS for the International/Asian version. If you do then I can’t help you. Lets start! THIS IS NOT A FULL THOROUGH REVIEW…JUST A LIST WITH OPINION.
1. CyanogenMod 7 ROM or CM7 is my absolute favorite ROM. Large community and a solid team of developers that support multiple devices. I recommend this one because it’s stable and there’s a large following. Cyanogen has two types of roms; Nightlies and Roms that are Stable. Nightlies are updated nightly and you take slightly more risk installing these because constant changes are being made. I have excellent battery power on this ROM; better than stock in my opinion. The stable ROM is confirmed to be stable and working.
2. Perception ROM by DesignGears. These people are pros at what they do and have made solid ROM for previous Samsung models. Now, this doesn’t have as big as a following and it still seems as though they’re fixing a lot of things that Cyanogen has already achieved. I don’t see a lot of screenshots but DesignGears always comes around. They’re out of beta so this is a very good thing. This rom is not my choice but it may be yours. Also the below screenshot is the only one I could find. It won’t look like that after install, the below picture is highly themed by the user.
3. UnNamed ROM <<< version will change with time. This ROM is very very popular among AT&T SGS2 owners. It should have been number two but I want to give each ROM a fair chance. What I like about this ROM are the options in the notifications bar which I didn't get with CM7. This ROM is confirmed STABLE, very stable and although it has had bumps in the road it looks like a solid choice. On the positive side the installation of this ROM seems to be slightly easier than CM7 in my opinion although the instructions are almost the same.
4. h8s2 ROM v1.1 ROM. I have never tried this rom but it’s working on the AT&T Galaxy S2 (sII). Look out for h8s2 because it looks nice. Follow Them @h8rift
5. Cognition X2 ROM by DesignGears. So I love every version of Cognition. This ROM is known for one thing and that is stability. It’s still considered beta because they are adding features. I don’t have this on my i777 S2 but I like where they are going with Cognition. Cognition has an enormous following but they aren’t as flashy as CM7.
6. Serendipity 8 ROM [2.3.4] <<< The version will change with time. Now I have never tried Serendipity but a lot of people love it. The people who have serendipity typically switch back and forth between Perception and Serendipity I have noticed. I haven't heard anything too negative about Serendipity. Look a little bland in my opinion but that could be because it's about stability and not about flashing graphics, etc. I can't speak too much on it because I've never installed it but it's a viable option for your AT&T Samsung Galaxy S2.
7. MIUI ROM. Okay with this ROM you are honestly taking your chances. They have a huge following with the Samsung Infuse 4G but there isn’t a really good port over for our phones. At this moment in time MIUI should not be on my list BUT hopefully someone will pick up where the originator left off. If you want to take your chances with several things not working on your phone then try. This ROM is known for being flashy with tons of graphics. I’d wait, your call.
8. GalnetMIUI ICS. Yeah, Ice Cream Sandwich. This is a little newer than the above. I don’t know much about it. Looks nice though.
-Brand new Framework (Android 4.0 Merged)
-Edited build.prop & updater-script
-Fixed home & search buttons
-Fixed Audio issue
-Added Nexus Prime Boot Animation
-Added Digital Clock
-Added Rom Manager
-Setup theme and saved as backup
-Removed FM Radio
-Removed MIUI Updater