I have tried Liberty 1.5, Apex 1.4.1, Rubix 1.9.7 Focused, and Fission 2.6.1.
I must say that Fission is my favorite so far, up until I started having random reboots and sometimes when I pressed the lock button, the screen would take about 30 seconds to turn on. It was fast at first but had been getting slower by the day. I'm currently reinstalling it, PITA setting stuff up again but w/e.
I was attached to Liberty cuz it was my first ROM, but it had its quirks. Didnt seem all that blazingly fast like everyone says either.
Went to APEX after Liberty, figured I'd try it out. Worked great, easy to use, but I had gotten used to the AOSP feel of Liberty already, so APEX felt kind of weird.
Installed Rubix after APEX, didn't stay on it for long cuz it was frustrating me how the apps didnt auto-download from the market. But it was blazingly fast, like unbelievable.
Then I saw this and went to Fission and love it.
Now my only question is why do ROMs run so well for the first 2 days then get slower and slower and slower? Its like what happens to my computer after I reformat and its super fast and 2 months later its slow as crap, but with the phone it only takes a week. Does the amount of apps you have affect performance? I find myself having to re-flash every week to keep the phone running smooth, and its taking way too much time for me to set up each time I flash.