I'll go roughly in order that I can remember.
I did watch Cosby show, though I wasn't a huge fan of Cosby. I liked Family Ties alot even though it had those cheesy "touching" moments I generally hate in sitcoms.

There's a reason why it launched Michael Fox's career. Night Court was pretty funny. It launched John Larroquette's career. Cheers was the best of the 80's lot however. And probably my favorite sitcom of all time.
The 90's brought about Seinfeld. Probably my second favorite sitcom of all time. Never had to worry about cheesy "touching" moments in that show. First season started off a little rough. I feel like they could have done one more season. But the last season was starting to get a little off track. I can understand why Jerry felt the need to pull the plug before it "jumped the shark".
Friends came out in the 90's. Alot of people make fun of it. It was just another sitcom. Most sitcoms are roughly the same. If you watch the old 50's ones, you realize they have been using the same jokes for over 50 years. What makes a sitcom work is the characters and acting. And the cast of Friends made it work. The only character I didn't like much was Rachael, but she had her moments.
Frasier. I admit I didn't like it when I first watched it. I was a diehard Cheers fan and was of the opinion spinoffs always suck. This one is an exception. I also didn't like the high-brow humor at first as I'm not from that culture. But it's actually quite funny.
I remember liking 3rd rock from the sun the first few seasons, but I kind of lost interest after that. John Lithgow really made that show work. Great acting by him.
Scrubs. The first few seasons were great, but I kind of lost intersest. That might be more due to my growing addiction to the computer and internet. Sigh. TV doesn't hold my interest as it once did.