I agree that
Sam is very friendly sort of name. I think it can stand alone, though it isn't my personal preference. I actually love
Samuel and, if I used it, I'd call him
Samuel, not
Sam.
Merely for the purpose of giving the bearer more options (not being able to predict whether he'd later feel he had only a nickname), I would choose a full name for "
Sam", provided there was a full name I liked. If not, however, I would not give a full name, just to have it on the birth certificate.
For fun, some "thinking out of the box" "
Sam" names...
GreshamSalomonAbsalom
Huh, that was harder than I thought it'd be. :)