I use the default bars.
72 buttons is plenty for all the keybinds I want.
Especially considering I can have a macro on "Q" which uses normal press, Alt Press or Control Press.

At one point I was using Mazzle UI, which is extremely artistic, but had 130 addons in the compilation.
I got tired of looking for fixes each patch.
These days I run with a few addons I really like and generally go for a more minimalist approach.

I use Auctioneer, Deadly Boss Mods, Diamond Thread Meter, Dot Timer, Jamba, Move Anything, oRA2, Postal, Prat.
That's probably about it.
Each is well maintained.