Someone would have to do a line count on that one day... I was always interested in that but never had the time. Anyway, Michelle had a much worse case than Jesse ever had, and as others have said, the reason he had so many episodes was that he went through so many changes throughout the series.
I've been doing a line count on a lot of the episodes that have been posted to Youtube, and Jesse is coming out with the most lines in most seasons. I'll list the season and the character with the most lines, and in brackets I'll put the number of episodes I counted in each season (I can only count lines from episodes that have been posted to Youtube, it's too hard to count lines off the tv).
Season 1 -- Jesse (12 episodes counted)
Season 2 -- Jesse (8 episodes counted)
Season 3 -- Jesse (5 episodes counted)
Season 4 -- Jesse (11 episodes counted)
Season 5 -- DJ (6 episodes counted)
Season 6 -- Stephanie (5 episodes counted)
Season 7 -- Jesse (10 episodes counted)
Season 8 -- Jesse (13 episodes counted)
Even though those results are not definitive, I have Jesse with the most lines in all but seasons 5 & 6. Even that might change as I count the lines on more episodes, as I havn't counted lines in any of the Jesse episodes from those seasons yet. I expect that Jesse will continue to have the most lines in the other seasons even as I count more episodes.