Here in no particular order are some sitcoms from the 1990s that I loved.   

i]The Simpsons (the 1st 7 seasons)-  In my opinion, the writing of the first seven seasons of this show is in a class all by its self .  What made the writing so great was that one had to have a good knowledge of literature, history, and pop culture to understand the jokes woven into the dialogue.  The first seven seasons of The Simpsons also portrayed the American family, work place, health system, education system, and political system in an unflattering way.  Homer, Marge, Lisa, Bart, and Maggie were not the typical TV family.  In decades past, when the children in an American TV family had growing pains they would come to the adults in their family for guidance.  Matt Goering would have none of that.  Homer was not the most supportive or responsible father/husband.  He often humiliated his wife and bullied his son.  Marge, hoverer, knew she was right and would wait for Homer to screw up so she could tell him so.  Homer would then admit his fault because, in the end, he really did love his family.  Bart was the irresponsible and disrespectful child, which many families had.  Lisa, on the other hand, was the overachieving and caring child, which many families wanted.  Now days none of the characters act like themselves and it is like a whole different show.     
Seinfeld     First off, Jerry Seinfeld did not do one second of acting during this show.  He didn’t have to because of the acting of his co-stars.  Dryfus, Alexander, and Richards were the ones who provided all the entertainment.  On other shows people treated one another in a mature way and learned a moral lesson at the end.  Seinfeld, on the other hand, used the characters to portray the worst in human nature.  In my view, Jason Alexander’s character of George Costanza made the sitcom.  What many people didn’t realize was that George Costanza was a very dark and demented man.  He was immature, inconsiderate, and inappropriate, in every way imaginable.  Seinfeld showed the audience why he was that way by bringing his parents into the show.  George came from a broken home where he suffered so much emotional abuse from his parents that he never would be able to relate to anyone in a positive, or meaningful, way.  People tell me that they were shocked when George “accidentally” murdered his wife to be with poison envelopes he picked out for the wedding.  Well, what did they expect?  Could you see a man (if you could call George Costanza fully mature enough to be one) like George being able to share his life with anyone at all on an emotional level?  In fact none of the four main characters were close friends they just used one another to get themselves out of bad situations, or ruin other people’s lives. 
The Drew Carey Show I loved this show because Drew Carey was such an easy character to connect with and root for.  Whenever Drew would try to find the right woman, or improve his financial status, his friends would foil his plan and Drew would be back at square one.  The one line zingers between Drew and Mimi were some of the best I have ever heard.  Lewis and Oswald were cool because they never had any life changing experiences.  They were always the same two stupid losers who seemed to be holding Drew and Kate back, but Drew and Kate never had the heart to ditch them.  I loved how Mr.Wick used Drew to intimidate the other employees because Drew was the only one desperate enough to listen to him.  Some have said that this show was on for too long, and I agree.  Nevertheless Drew and the good people at WB need to get a season one box set out soon. I own the small six episode collection that came out the other year, but it has no special features of any kind. Why, oh why, did TBS pull Drew Carey off its afternoon lineup, and replace it with Yes, Dear?  That show is full of rejects.
Third Rock from the Sun- John Lithgow is the man!  You just can’t go wrong with any movie he’s been a part of.  In fact, if anyone else had played that role than I wouldn’t have even bothered with this show at all. Well, Jane Curtin was pretty funny as the “straight character” of the cast too.   
Frasier- Frasier’s dad, and Daphne, was the heart and soul of the series. Marty Crane couldn’t have a single moment in his son’s apartment without getting into a heated conflict of interest.  It was in those conflicts of interest where the audience saw just how far apart Marty and his boys stood on every conceivable issue. Daphne was funny because she always had to officiate the conflicts in the home like a nanny. Niles and Frasier had a very interesting relationship.  Niles was always trying to one up his big brother, but he also looked to Frasier for guidance. I think the point of the show was adults trying their best to do the proper thing in every situation, and failing miserably.     
So there you have it, my five favorite sitcoms of the 1990s which stand head and shoulders above any sitcom on TV right now.  I can’t wait to read your feedback. 

I liked all of those shows except Seinfeld.

I have the first season of Third Rock From The Sun.  Loved that show. :)

The Simpsons is a classic but I wouldn't call it a "Sit Com".