I loved using UA, but I found that it was easier for class combinations to use Dragon lance Adventures for class and race rather than using the UA classes as they were written (aka, instead of Cavaliers we have Knights of Solamnia, and in addition, level 18 is a hard cap for EVERYONE...though demi-humans can still have level limits...some of them particularly high comparatively to the original PHB).
I liked that races still had limitations and level limits as well as class limits...more restrictive than WotC D&D (which I think detracts from flavor and not exactly my favorite thing to come out of WotC...but that's a highly unpopular opinion), but loose enough that almost everyone would normally be happy (afterall, how often are you really going to have a group reach those level limits listed...and if they do...that's a dedicated group that's been playing for a while).
Or, we'd go with OA, or combine some elements from OA (for example, using the OA version of the Barbarian made it easier to actually have barbarians in the group, though still particularly difficult if you consider Wu-Jen and Magic Users the same class restriction, at least we could have Clerics in the Party though!)