If you want to stay as near stock as possible but want faster speeds and slight improvement over stock TouchWiz ROM, you can try MadMack ROM for the Galaxy S2. I kinda like this ROM a lot as I like the stock TouchWiz but MadMack takes it to another level with blazing speeds.
Download ROM here:
Download MadMack ROM
Donate to original developer here
Don’t know how to install a new ROM? Look here.
Don’t forget, you need to root your Galaxy S2 and make a backup of your ROM first before installing new ROMs!!! Also backup apps!