My thoughts:
50's: I Love Lucy
60's: The Andy Griffith Show
70's: Three's Company
80's: The Cosby Show
90's: Roseanne
00's: Friends
2010's: The Big Bang Theory

1950's - The Amos 'N Andy Show
1960's - Gomer Pyle USMC
1970's - Sanford & Son
1980's - Newhart
1990's - Married with Children

These would be my actual choices if not limited to sitcoms

1950's - Alfred Hitchcock Presents
1960's - The Twilight Zone
1970's - The Six Million Dollar Man
1980's - St. Elsewhere
1990's - Picket Fences

May not be considered "the best", but these are my absolute favorites from each decade:

50s: I Love Lucy
60s: Green Acres
70s: The Jeffersons
80s: Mama's Family
90s: Family Matters
00s: Will & Grace
10s: 2 Broke Girls

1950s I Love Lucy
1960s Family Affair
1970s Barney Miller
1980s Benson
1990s Frasier
2000s Corner Gas
2010s The Middle

1950's- I love Lucy
1960's- Green Acres
1970's- Sanford & Son
1980's- Mr. Belvedere
1990's- Friends
2000's- King of queens
2010's- Mike & Molly

1970s Barney Miller

That's exactly the one I would choose for the 70s. I must admit that I don't have any choices for the others.

Here's my list...

1950's...I Love Lucy...

http://thegrassskirtblog.com/wp-content/uploads/2011/08/cast.jpg

1960's...The Dick van Dyke Show

https://chitownstarconnections.files.wordpress.com/2011/12/dvd-show-cast1.jpg

1970's...All in the Family...

https://pmcvariety.files.wordpress.com/1971/08/all-in-the-family.jpg?w=670&h=377&crop=1

1980's...Gimme a Break!...

http://www.sitcomsonline.com/photopost/data/983/3gimme.jpg

1990's...Home Improvement...

http://www.glamour.com/entertainment/blogs/obsessed/2012/11/15/1115_home-improvement_ob.jpg

2000's and 2010's...I don't really have one...ohno:ohno:ohno:ohno:ohno:

1950's- I love Lucy
1960's- Green Acres
1970's- Sanford & Son
1980's- Mr. Belvedere
1990's- Friends
2000's- King of queens
2010's- Mike & Molly
Sanford and Son is my favorite too.

1950s-I Love Lucy
1960s-?
1970-The Odd Couple
1980s-Facts of Life
1990s-Seinfeld
2000s-Friends
2010s-Modern Family

50s--I Love Lucy
60s--The Dick Van Dyke Show
70s--The Mary Tyler Moore Show
80s--Newhart
90s--I don't know
00s--I don't care
10s--WGAF

50s- Leave It To Beaver
60s- ?
70s- Three's Company
80s- Cheers
90s- Seinfeld
00s- The Office?
10s- Parks & Rec?

-Doing this little exercise made me realize 80s & 90s sitcoms > All

1950's- I Love Lucy (1951–1957)
1960's- The Andy Griffith Show (1960–1968)
1970's- Happy Days (1974–1984)
1980's- Mama's Family (1983–1990)
1990's- The Wonder Years (1988–1993)
2000's- Pass
2010's Pass

50s: Honeymooners
60s: Andy Griffith
70s: Threes Company
80s: The Love boat
90s: Roseanne

I dont have any after the 90s I like... All rubbish in my opinion..

1970's: The Mary Tyler Moore Show
1980's: Family Ties
1990's: Frasier/Roseanne
2000's: According to Jim

1950s - I Love Lucy
1960s - The Beverly Hillbillies
1970s - Tie between Three's Company + Laverne & Shirley
1980s - Cheers
1990s - Frasier
2000s - Tie between Malcolm in the Middle and The Bernie Mac Show
2010s - TBD

50s- I Love Lucy
60s- The Munsters
70s- Happy Days
80s- Cheers
90s- Seinfeld
2000s- Curb Your Enthusiasm

My list of best tv shows that aren't sitcoms

50s-???
60s- The Twilight Zone/ Alfred Hitchcock Hour
70s- The Mod Squad
80s- Matlock
90s- Murder She Wrote