Are you likly to fill it with movies or RAW camera images, if not get the 32gb as 64 is actually quite a lot when you are just looking at data and not a fat install of windows or OSX.
I got a 64 put LOADS of stuff on it, programs, 2000 books etc and used less than 2 gig...!!!
Then i sold it.....
I would advise you to buy it from Apple direct because they give you 14 days to just hand it back, i got mine from PCWorld as i did not want to wait and they do not honor that policy....
:-(