This list include some of my personal choice, but is mostly based on what I've seen other members say. I even included shows I am not a fan of be fair.

40. The Hogan Family
I have never seen, but I have heard good things about it
39. Designing Women
I am not a fan, but I will give it props for good writing
38.Wings
Again, I am not a fan, but I will give it props for the writing
37.Chico and The Man
I've never seen it, but it gets an A in diversity
36.Roseanne
Not a regular viewer of it, but it is really funny.
35.Mr. Belvedere
Good, clean family sitcom
34.ALF
Surprisingly good for a show about an alien
32.Kate and Allie
Handled reality well
31.Happy Days
provided a good contrast to the relevance sitcoms of the 70s
30.Three's Company
Not a fan, but it gets points for edgeness
29.Little House on the Prarie
A true reality show at times
28.Taxi
Writing is intelliigent and funny
27.Welcome Back Kotter
Real and funny
26.What's Happening
Hilarious and one of the best of the 70s
25.Laverne and Shirley
I like the slapstick
24.M*A*S*H
I never got into it, but the writing is good
23.WKRP in Cincinnati
Hilarious
22.Empty Nest
One of the most underrated sitcoms of all time
21.Hill Street Blues
I like the gritty realism
20.Murder, She Wrote
Great mysteries that keep you guessing
19.227
First black ensemble comedy. the writing and acting are great
18.Simon and Simon
Includes sleuthing with action and some comedy.
17.Cosby
The ensemble is great and the writing is smart and funny and the same time.
16.Dallas
Not a fan, but the storylines appear to be well written
15.Diff'rent Strokes
Hilarious
14.Gimme a Break
A family show with edge
13.Growing Pains
Hilarious although a copy of Family Ties
12.Amen
The first comedy about a church. acting and writing is great.
11.Leave it To Beaver
A good family show
10.Mama's Family and Night Court (tie)
The comedy is great and all the characters are funny
9.I Love Lucy
Enough said
8.Who's the Boss and Facts of Life (tie)
family comedy with a edge. FOL is hilarious
7.Family Ties
Amazing writing and acting and hilarious
6.Good Times
Reality and comedy mesh well. the acting is good and it tackled a lot of serious issues
5.The Golden Girls
One of the best series ever. intelligent writing and great acting
4.Sanford and Son and A Different World (tie)
Enough said.
3.The Jeffersons
Well written and a groundbreaker
2.Cheers and Mary Tyler Moore (tie)
Smart and witty
1.All in the Family and The Cosby Show (tie)
No words are needed

honorable mentions:
Alice
Green Acres
Rhoda

The worst

Full House (sorry, fans)
Friends
Seinfeld
Boy Meets World