For my style of play in the upper difficulty levels, I value Financial and Organized (and Aggressive to a lesser extent) the most. Industrious, Creative, and expansive I value the least. Spirtual and philosphical are in the middle; useful, but it can depend on the style of game I want to play.
Given this value system for traits, in a vaccuum (without starting techs and UUs) my least favorite leaders are (in ascending order of quality):
Cyrus
Bismarck
Isabella
Louis
Peter
Cyrus is up at the top because of the mid-late game impotence of cre/exp. He could be powerful in the beginning when you factor in his UU, but I'm generally very underwhelmed.
Bismarck, I must say, I've never played. If you factored in UU's he'd probably actually be worse than Cyrus in my opinion (the number of games I've taken to tank warfare is very low). His trait combination is a bit better, but industrious is generally not overly useful on the upper difficulties unless paired with aggressive for the cheap forges (I like napoleon).
Isabella has the moderately useful spiritual trait so she can't be all bad. Plus, the conquistador can have uses. She seperates herself from the bottom two a bit because of those two reasons. Still not a leader I'd choose, given the choice, but I have won a game or two with her.
Louis really doesn't have much going for him. His trait combination is very difficult to make effective use of. Actually, though, one of my first emperor level wins was with him. Though, I later found napoleon to be superior in most every way, the cheap forges leading straight into a fairly versatile UU was something I appreciated. Again, though, playing as Louis makes the game a bit more difficult than it otherwise would be in most cases.
Peter is another leader I can only talk about on paper. I may have played as him on noble when I was first learning, but the random number generator hasn't drawn his number in some time for me. Philosophical is a genuinely useful trait and actually has some synergry with expansive (the only trait that really goes well with expansive). Your GP farms are that much easier to create. I also considered Hatshepsut for this spot, but decided my opinion of her is currently tainted by a recent losing effort on an island start (something she's not terribly adept at handling).
And, I know you didn't ask for it, but my top 5 are probably: George, Huayna, Elizabeth, Toku, and Mao.