DaCostaBR: I was thinking of how hard it seems to be finding an actually funny sitcom, which gave me the idea to trade recommendations and warnings to stay away from in a thread.
Best - It's Always Sunny in Philadelphia: It's been going on for 11 seasons and it's still funny. It really shows how to make a good comedy you don't need relatable characters, or a decent budget, you just need funny jokes, and this show about four sociopaths in bar has that in spades.
Worst - The Big Bang Theory: I could complain of its portrayal of nerd culture, but if I'm going to be perfectly honest, if I actually found it funny none of that would bother me. That's its biggest crime, it's not funny. I don't want to be too harsh on it, I think a show like this always exists. A show that's generic, safe, full of laugh tracks, not very funny, yet is the most popular thing on TV. Now that's TBBT, 10 years ago it was Two and a Half Man, 10 years before that it was Friends (I know Friends has a lot of fans, and I fully expect people to list it here under best sitcoms, but personally I'm not a fan). I guess the biggest crime for me is for a show to be mediocre.
When I saw this thread I was going to mention Big Bang Theory, because it's the first title in my mind that is for some inexplicable reason adored, despite being a bit crap. Like you say, it simply isn't funny. Oh, and have you seen some of those videos where the limitless canned laughter is removed? Embarrassing stuff, it really is. Two and a half Idiots is crap too. I really don't understand how people can find this garbage funny.
Friends I actually liked at the time, it was genuinely funny. But when it comes to great sitcoms, I think it's hard to top Seinfeld. Probably hasn't aged great as there are some jokes and such about contemporary people, but it's still brilliant.
I liked How I met your mother in the beginning, but as the seasons passed by, it got increasingly cringey and annoying. Barney was the one light spot, but when they even messed him up... good grief, and good bye. Should have ended it sooner.