Stuf is my current frame addon of choice... I spent a long time using Gypsy (a looooong time ago) and then Pitbull.

With a handful of custom LUA tweaks to add things like showing my current XP/max XP, better pet happiness (and pet XP), and icons to show when I'm resting/in combat (because I didn't like the default ones), I'm always happy with what I can get done with Stuf.

That being said, I can never keep my UI looking the same for more than a month or so... I tend to enjoy trying out new layouts almost as much as I enjoy playing my Shaman...

I have tried stuf and scrapped it in favor of pitbull. At the time the unit frames wew not updating frequently enough on stuf and I was used to the quickness of xperl. (Xperl had its own problems that seemed to be fixed with cata content.) After a short stint again with xperl, ended up going to pitbull for the similar functuinality of stuf but with less fluff (imo) heck... been days since I have been in wow, can't even remember if I decided upon anything.
Overall, there are lots of uf addons that are good and most each has something someone can't do without. I love that I have choices.
And similar to nipah I tend to change my layout monthly or so, tossing out some addons just to try others.

The marking bar, gonna have to check up on that one, last addon I was using broke.

I use Perl Classic UF. Nothing too fancy, nice skin, everything I need, very little that I don't. Things it doesn't do (or doesn't do the way I want) are provided by separate addons.

I switched to chocolatebar once fubar stopped being updated, it's pretty much exactly the same addon.