I've seen both (mostly) and I definitely see FK elements in Angel. esp. the first season of Angel.
-Angel and Nick have (pretty much) the same car, which is fun!
-Both keep nothing but blood in the fridge.
-Both do want to be human again, to atone for their pasts, but while Angel has the mystical prophecy thing, Nick seems to rely more on science -- which is weird, since FK vamps are definitely more magical than Angel vamps (Nick can hypnotize people, is sometimes telepathic and can fly!!)
-Darla on Angel is kinda similar to Jeanette on FK...except I think Nick and Jeanette have way more chemistry and a way more interesting relationship than Angel and Darla. Both Jeanette and Darla get to be human for a while, though, which you might call borrowing!
-If you watch the episodes in season 1 of Angel with Kate the detective, you get a good feeling of what FK's like. Nick is a cop, while Angel only helps out, though. So maybe Kate is similar to Tracy Vetter on FK...both are really really blonde!
-Both Angel and Nick have a preference for long coats (but then so do most vampires!!)
-AND, the crowning glory, an FK actor actually guest stars on Angel -- John Kapelos who played Schanke -- in the Angel episode with the Hyperion hotel and the Shining-like fifties flashbacks I think that's like a little salute from Angel to FK!
I bet I'm leaving out a bunch of things, but that's all I can think of for now. Not that I've ever actually thought much about this before, or anything like that!
Oh, and I think I like FK better because I saw it first and it's a little bit darker. And it has LaCroix! Angel's dark and funny and FK's dark and more morally ambiguous, none of this soul/no soul business. Also, FK has more history (Nick meets such notables as Joan of Arc and Jack the Ripper), but Angel is definitely more stylised -- and the action is better!