I have to go with Monkey-Faced Leia as the worst figure. The likeness absolutely sucks. I bet Carrie Fisher winced when she first saw it. There is a similar thread at POTF2.com where it was mentioned that the figure looks like Anthony Kiedis from the Red Hot Chili Peppers. You make the call:
R5-D4 might have been okay if they'd made him "normal" like R2-D2 rather than putting that hokey Concealed Missile Launcher in there. I didn't care for how they sort of made stuff like this up. They did the same in the Deluxe line with Boba Fett, Han Solo, Stormtrooper... A license to make Star Wars toys is not a license to just start making things up and slapping the Star Wars name on it.
The "buff" look was pretty dumb, and it took them a while to finally give it up, but you have to remember that at the time this was a brand new line of toys and they were trying to capitalize on the popularity of things like Power Rangers and Spawn. I think they were going for a comic book feel to the line...