wav or aiff

I'm having some dialogue recorded in a studio. I usually tell them 48K, 16 bit. I've successfully used .wav and aiff files interchangeably in the past, but does FCP 5 in fact prefer AIFF files?

Any gotcha's to look out for?

WAV and AIFF are different containers for the same thing, linear PCM audio.
Quicktime supports both so there shouldn't be a difference. I would just go with AIFF, because it's the convention on a Mac. In any case, if there's a problem, you can convert one into the other in seconds.