The family guy ones can vary with me. Sometimes I find them brilliant and can't stop laughing. Other times I just want to kill the writers by impaling them on a flag pole (with the glorious and wonderful Union Flag raised.)
Case in point - the one with Nigel, the pub owner - I hated it...until I saw the hilarious resemblance to the Anti-Christ, Tony Blair. Then, it became funny.
The American Football ep - where Peter moves to London though - not the best.
I think the best family guy Brit stereotype is a small bit clip, in passing reference. (I think its )in Big Fat Paulie, after a mob guy gets killed in a drive by, Peter suggests moving to England because;
"aaw, the worst they gotta put up with is drive-by arguments!" - que what is possibly my favourite clip, of said argument.
To be fair though, look at how most Brits label Americans - gun loving, bible waving, etc...