I basically use my raid UI, which has some drawbacks that I haven't found a reliable way to overcome yet.
http://www.virtuousguild.com/images/vecui2.jpg
(This picture is ANCIENT...)
Problem areas:
1. No Arena mod. I'm thinking of dropping Proximo where Omen is, and just toggling between them for PvP/PvE.
2. Can't see target buffs. I can enable it in Pitbull, but I don't like how it displays, and I'm pretty much at a loss for how to improve on that.
3. Health display issues in Pitbull. This is a recent problem I've had, and one I don't know how to correct (I think something changed in the last revision of Pitbull) - basically, I want in-party targets to display absolute health values (see self/target-of-target), but hostile/out-of-party targets to display percentages (see target). I had this working before, but now I end up with either estimated absolute health values for bosses, or percentage values for party-member targets. Halp?
I should also point out that I have a focus frame just to the left of the buff bars, not shown.
I rely on Grid for party health information, since I'm not a healer and can't do jack about debuffs - all I need is an at-a-glance idea who's alive, and how alive they are.
For anyone who does both PvE and PvP, I think the critical thing is to minimize differences between them - I try to keep my keybinds similar, my UI similar, etc. I have enough adjusting to do with managing different cooldowns, talents, trinkets, abilities, gear, etc. - having my entire display change would probably kill my interest in PvP altogether.