Honestly, I totally forgot about this ROM, Ultima ROM for months! The latest version of Ultima ROM is probably one of the most customizable ROMs for the Galaxy S3 GT-i9300 with literally every kernel/launcher available with its AROMA installer.
Ultima ROM combines some of the best features like multi-window (enabled for all apps using Multi-Window Control app), HD YouTube app with Screen-off play, 5×6 TouchWiz launcher (if you want TouchWiz), 5 different lockscreens, lockscreen torch, auto call-recording, long-press to kill apps, and lots more. Best of all, I like how Ultima ROM comes themed yet its subtle, you barely notice it’s there. I personally prefer slightly themed ROMs and Ultima ROM is an ultimate example of that.