Just noticed this thread, thought I'd add mine.
Clickie
First of all, I wanted something that looked good. I'm staring at this interface 5 hours during raids, it has to appeal to the eye. Then, I wanted as little bars as possible. And ofcourse, centralisation. A good UI will have all the necessary information bundled together.
Minimap and chat in the middle, with UI frames to the sides.
Totem durations and bosswarnings on the topright, together with Yata (I will often move my eye towards that spot to refresh totems anyway, so it's a good position to bundle it all.
My raidframe is on the bottomright, above my targetframe.
And final: Little memory usage. I hate red memory numbers.
I do need to add a castbar of some sort somewhere, though.