I'll kick it off....
American Sitcom - The Fonz
British - ???
Which Sitcom Character Had The Most Sex?
American: Quagmire
British: Fran from Black Books. That chick get around.
Joey from Friends probably. He shagged a woman from every country according to his spin-off series.
Blanche Deveraux.
Dorien Green - Birds of a Feather
Mandy Wilkins - Game On.
Oh and of course Griff's suggestion above. Hopefully the one who used to be in Hollyoaks. Grrrrrrrrrr!
By the way, I think this is in the wrong forum. EEEEEEEEEEEELLLLLLLLLLLLLLLLIIIIIIIIIIIIIIIIIEEEEEEEEEEEEEEEEE!
As a contender from a US sitcom, Mrs Dubcek from Third Rock.
Seymour Butts.
Alan B'Stard had a lot. And it didn't take long so maybe he had the most simply due to time constraints/efficiency 
Dan
Rose from Keeping Up Appearances
US - Roz from Frasier
Brit. - Mrs. Slocombe's pussy, Are You Being Served?
Definitely Joey. Remember this?
"Joey, you've had a lot of sex, right?"
"What, today? Some. Not a lot."
Sam Malone - Cheers.
I always imagine Dr Lucien Sanchez (Matt Berry) in Darkplace got quite a lot of action. He was smooth.