I rarely watch TV much less comedy TV, but Curb is hilarious. My girlfriend has the first season DVD and we've watched it more than once. It's fantastic and totally re-watchable.
Sunny was cool for a while, but I find the later seasons are really stretching the premise of four friends being dicks. I liked it a lot better when it was just them being slightly ridiculous, but after like season 3 everyone started becoming really extreme versions of themselves. Kind of like how Homer used to be just an oaf, but eventually became someone totally clued out. Again I only saw a handful of seasons of Philly on DVD, so I don't know how anything past the fifth season fares (or is faring; is it even still on?). Quality doesn't tend to U-turn, though, so I wouldn't be surprised if it just became more and more of what I don't like.
A lot of people still swear by it, though.