Best [ROM] for Samsung Galaxy2, until the moment I wrote this, is Stock ICS Samsung ROM!
Best Samsung Galaxy S2 [ROM] for battery, lightning smoothness and beautiful interface, but not for gaming it's Lite'ning [ROM]
Best Samsung Galaxy S2 [ROM] for smoothness, beautiful interface, and best ROM customization, good gaming conditions, but not for best battery, it's Resurrection Remix ICS.
You can read more details here Why I made this top Best [ROM] for Samsung Galaxy S2 .
Custom [ROM] ROOT