As far as Stewart goes....I've never been a big fan of his, my dislike of him actually started waaaaaaay back when The Jon Stewart Show debuted on MTV, he wasn't my cup of tea then and he still isn't. I've never found him all that funny either. Although personally I like him, he's always good on Howard Stern.
As far as Maher goes, I find him almost unbearable at times as well, but I loved the format of his old show and being a kid who grew up watching stand up specials all night on on HBO and Showtime, I loved all his early guests like Carlin, David Brenner, Dice, Robert Klein, Richard Belzer, Richard Lewis etc. and I've just kept watching out of habit I guess, but I definitely prefer the old format to this one.