I like Fin, but really only as a nickname for
Finlay. And for a boy only.
I think
Finnegan is cute, but just too Mr. Dress-up for me (this is a reference that will only be an issue if you happened to be a kid in Canada in the 80's)
Phineas is alright, but I have kids, so the whole
Phineas and Ferb thing is a bit much for me.