Unless the male is supposed to be a ladies man never have your leads too good looking.
There it is. Think about it. Friends [including Joey] King of Queens, Everybody Loves Raymond, Not Going Out, Men Behaving Badly, The Office, Only Fools And Horses, The Green Green Grass, Terry and June, Spaced, The Big Bang Theory, My Name Is Earl, and on and on and on.
This came to my attention when I happened to see and episode of 'Freddie' starring Freddie Prinze Junior [ cancelled] The guy is good looking. But not a womaniser. Result? Ratings death.
On the other hand of course the female leads should generally be as attractive as possible in a ''girl next door scrubbed up nicely'' kinda way.
Lines that might get a belly laugh from a geeky Ross or a gawkey Rodney just don't get the same reaction from young chisel face Freddie. Women might want to be with him but men want to punch his lights out. There's half your demographics gone right there.
Seems to me that if casting is important for drama it is vital for comedy.
Moral of the story - cast ugly for better line appreciation. Don't get me wrong, I'm not saying any of the above males fell out the ugly tree and hit every branch on the way down. But they ain't the Elle McPherson of Friends [or any one of those dork's girlfiends with the possible exception of Janice] or the Pamela Anderson of Stacked.
I'm not a comedy writer so take the above with a pinch of salt. But to me comedy is usually about the underdog. Save the pretty boys for the Byronic heroes.