What C. M. Burns said, and I’ll add Seinfeld and The Simpsons to that list.
I will admit that I had pretty much gone off sitcoms by the '90s, and was living overseas during much of that time, so I’ve only seen multiple episodes of maybe ten or so of the ones on the list, and most of those only in syndication.
Frasier not only matched it, but bested it, by a significant margin too, imo.
Absolutely. It’s hard to describe how fresh their approach was to someone who’s seen the show their entire life. It was a quantum leap.
Hardly. I’ve never laughed like I meant it watching Frasier. Not once.
Even today, a pale shadow of its former self, *The Simpsons *can turn a comedic phrase and elicit a belly laugh as well as any show on television. It’s always had a tremendous sense of the human condition, and uses the fourth wall with a tried and true intimacy that is nearly unrivaled.
Now that’s comedy.
Or denial.
Or a real dearth of anything on TV that’s all that funny.
Outside of Modern Family, of course 
I recall a visit home to Texas from Thailand in 1990, and a buddy told me I had to watch this fantastic new show he’d been videotaping. He didn’t think it would last long, because it was too clever. That’s how I saw the first season of The Simpsons. We and several others watched it non-stop, in a , heh, slightly altered state. I was blown away. It was not like anything.
Some time later while visiting Santa Fe, I noticed it was almost time for the show to come on one evening. Went into a bar that had a TV playing and asked the bartender if he could change the channel. Felt somewhat ridiculed when he said, a little condescendingly: “Sure, you can watch your cartoon.” But he did change the channel.
I don’t think I’ve watched a single episode in the last 10 years or so. Maybe 15 years. It’s on cable here, but we don’t subscribe to cable. DVD sets are available, but at this point it feels a little overwhelming how much I’ve missed. Will have to pick up a set of episodes sometime.
Say, if The Simpsons is included in the poll, why not South Park?
I voted for several, but Frasier is my favorite of all these…truly great writing, consistently good throughout its run (save for one bad season), and wonderful characters. I was in love with Daphne… 
The Wonder Years is perhaps my favorite show of all time, and while I voted for it, I definitely would not characterize it as a sitcom…it was a drama.
You got a lot of great ones on that list, but you did forget Sports Night. I loved that show. Watched it on DVD six months ago and it was still good.
I’ve never been a big fan of sitcoms, but two of my favorites that started in the late 90s were both left off the list. **Two Guys and A Girl **(Firefly fans, check it out. Nathan Fillion’s in it) started in 1998, and The Norm Show started in 1999.
Roc was a pretty good sitcom from the 90’s, although it went serious now and then.