I agree about Ohmforce in that their funky skins are hard to accept, but once you do, they are actually pretty ergonomic and easy to use. I do think that Ohmboyz is kind of ugly though, and Ohmicide is decidedly not ergonomic.
U-he and Fabfilter do stick out in my mind as having the most 'pro' looking guis, graphics wise. The saturation levels are fine tuned, the colors have heirarchy to them that corresponds to the controls, etc. They can be stared at and used for hours and hours.
Personally, I will always sacrifice a tiny percentage of ergo usefulness for a pretty picture. Its just necessary when spending so much time with a thing.
Considering both sides of the coin, my all time, #1 with a bullet, without a doubt:
Jobromedia - the GUI for the upcoming Rez 3 is higher contrast so it will hopefully be much easier to read for those with vision problems or lower contrast/less vibrant monitors. 
