Well for starters I have to be blunt. To hell with the haters, Superman's costume is cool! As for his disguise it's at least as believable as a guy fighting in alleyways in a halloween costume and not getting shot in the mouth or a radioactive spider bite not killing you. Besides, the people in the story do now know what the reader knows and they don't see Superman up close all the time. I think it only starts to stretch with the Daily Planet crew and especially Lois because she sees both men up close all the time, but with Lois that's part of the comedic and romantic irony. The idea that Clark could be anything more than what he seems on the surface is so far out she doesn't make the connection. In the hands of lesser writers this makes her come off as a bitch but done right it's fun.
The rest of my top picks are: There's many that I like but these are my favorites.
Spider-Man
The Flash
Batman
Captain America (as in Steve Rogers and with wings on the mask included)
Wonder Woman
The Neal Adams redesign of the Robin costume for Tim Drake
The Worst: Simple fact is that there are too many to mention. There are hundreds of characters, especially obscure ones, and let's face it the 90's gave us some real stinkers. Liefeld characters alone could make up this list but for my list I'm gonna stick with ones people might be more familiar with.
Wolverine
Spawn
DiDio era Mary Marvel.
The Scarlet Spider
The current redesign of the Robin costume for Tim Drake.
Superboy's Joe Schmoe Wednesday at the Comic Shop look. Not to say it isn't a rockin shirt but come on!