The super-short Season 4 bob was my favorite, for some reason. Less red than Season 5, but still pretty cool. I consider the Season 4 bob to be its own hairstyle, seperate from the others. Not that I spend lots of time analyzing Janeway's hair or anything... oh, wait, that's a lie.
Next to the bun, I liked Season 6 the least. Looked like Janeway got into a fight with a bottle of Aqua Net and lost!