One of the most popular and better aftermarket ROMs for the Galaxy S2 right now in my opinion is the Batista ROM for the Galaxy S2, it comes with minor tweaks to the UI (although still pretty much Samsung TouchWiz UI), 1.6Ghz overclockable kernel, and other goodies. I think this is the best Galaxy S2 ROM out there right now.
Galaxy S2 Root
Once you’ve rooted your Galaxy S2, you will probably want to try out several different ROMs, which will give you goodies like longer battery life and allowing your phone to be much more customized than stock.
Before we begin, make sure you’ve made a backup copy of your current ROM, you can see How to backup/restore ROMs on Galaxy S2.
Once you’ve made a backup of your current ROM, you will also want to learn how to backup and restore with Titanium Backup app as this method will allow you to quickly restore your apps when you install a new ROM on your Galaxy S2. (The ClockworkMod method backups up your WHOLE system including the ROM itself so you need another method to restore your apps such as this Titanium Backup app when installing new ROMs.)
For those of you who’ve recently rooted your Samsung Galaxy S2 Android smartphone, you will probably want to learn how to backup/restore ROMs on your phone using ClockworkMod Recovery. By backing up your rooted ROM, you will have an insurance in case something goes wrong in the future such as bricking your phone while installing a new kernel or ROM.
If you want to take the most out of your Samsung Galaxy S2 smartphone, you will surely want to root it as you can get cool things like free wifi tethering, overclocking your phone’s CPU, make complete backup of your ROMs and more.
For Mac OSX, you can use Heimdall instead of ODIN, please see How to Use Heimdall for OSX Video.