If you're going to pick out the five most "representative"/important '90s sitcoms, what would they be and what would make them representative?:

1. The Simpsons-This show sort of defines the '90s sensibility: quirky satire combined with a real "heart" and thoughtfulness, irony (but not overmuch), sardonic humor, and a hatred of snootiness and the rich.
2. Seinfeld-Another show defining the "decade about nothing." In some weird way, it gets another point of the '90s: that the point of the '90s is trying to find even fleeting meaning among the nothingness.
3. The Fresh Prince of Bel-Air-One of the engines bringing black hip-hop culture (in a tame form) to the mainstream. This show also screams '90s: it's feel-good, and the styles are 100% '90s. Watch the show based on seasons and it's a pretty textbook example of what's in then (for example, the 1995-1996 season styles look very normal and mid-'90s, whereas the 1991-1992 season screams early '90s.)
4. Friends-A Gen X TV show...the corporatized, Gen X Seinfeld.
5. That '70s Show-'70s nostalgia and the '90s.

Runner-ups: Full House, Frasier

Step by Step - Like a Brady Bunch for the 90's. The divorce rate in America was (and still is I bet) steadily rising. You basically had many different personalities, unrelated by blood but still a family, interacting with each other. It was also very 90's fashion consciuous. It was a reflection of the exploding ste-family in America and making things work the untraditional way.

Boy Meets World - Pretty much runs the gamut of the 90's, capturing both early, mid, and late periods...though probably more mid and late since the show premiered in 1993. In the early 90's you had the basic bully problems, self image problems, first crush etc, all in a 90's world. Later the show tackled serious family issues...divorce, moving away some, alcohol issues, interracial dating (which was more common and accepted in the 90's)

Family Matters is very 1991.  Boy Meets World defines the mid '90s.  Friends is very late '90s coffee culture. Seinfeld defines the '90s zeitgeist. The Simpsons IS the '90s.

Oh yeah, and I forgot Home Improvement...that show defines '90s family life. The '90s were very eager to dissect themselves compared to the '80s.

Would Bevis and Butthead count as a sitcom?