From a personal standpoint, I'd have to go with the IC title. As goofy as this might sound, everything about the title just seems to mesh very well together. The symmetry of the title plates just match up really well, the plates themselves are shiny and lustrous in appearance, the white sets it off and gives it this...I dunno...maybe a "clean" sort of overall look.
The WWE World Heavyweight Championship just seems to be lacking in grandeur, in my opinion at least. The "World Heavyweight Championship" wording size and style just seems kinda blah. There's no real style or pizazz to it. I prefer the new logo over the scratch logo, so that's an improvement. However, the biggest thing that gets me is that what luster the center plate has is dimmed by the leather strap of the belt. I'll take it over the spinner belt any day of the week though.
I've got no problem with the United States Championship. Has a decent little combination of new and old school about it. The red, white & blue motif doesn't overpower things, it's in a good balance.
The WWE Tag Team Championship belts are kinda strange. Some don't like 'em, but I've liked the coloring. It's different and I always thought that the Roman Centurion helmets standing back to back was a nice little bit of symbolism. Two comrades standing back to back, taking on all comers, etc.
The WWE Divas Championship is just...well it's just friggin' ugly in my opinion. There's no symmetry to the plates, the coloring is just lousy and the center plate looks like a friggin' butterfly. The championship looks....well...it looks downright girly for my tastes. Yes, I know it's a title for women, but it looks like an accessory a 10 year old girl would find packaged up with a Barbie doll.