Well my expernce with the three, Also my setup is UD Watermarked ADW with Galx S theme
Steel = Srry havent tried it yet but will soon
CM6 = Loaded just fine and has some improvements from the previous version. I ran into so FC issues that seems to be in the rom Not the Kernal, Also i noticed the redraw issue that is in Froyo but it seemed to be real bad in my CM6 setup. (could be ADW & Not Froyo's fault)
UD 7 = so far i would say this has been the most stable rom i have tried & i have tried almost all (Steel is new to me) along with the watermark theme & ADW the redraw after hours of use is about 5-25 sec when coming out of an app to the ADW home screen, Minfree helps alot with this as well, As for some of the other ROM/Froyo issues, Wifi at my office & at home work with little problem (had major issues with this in Lit mod, BB, CM, Ins, & Chevy1)
Except the issues yesterday with Themes I think the UD 7 is the best right now & between Goodies & custom scripts is what made me lean to the UD and all its goodness