It depends...
fat32 is the natural choice for simply having stuff...movies, music, books, etc...as storage for your NIT.
I suggest freshly formatting a card on your pc with a format utility..I believe I mention one of the best with a link to it ...it will work on win7 as well...esp. a new card before doing anything with it.
If intending to run an os off a card...precautionary 1st step is to format to fat32 (just in case) then follow the walkthrough for the easiest method of getting everything set up.
It's all explained thoroughly and simply...
the vid walkthrough should help as well...
if you have any issues that can't or aren't explained thoroughly...
tell me and I'll give you a hand in whatever way I can.

64 gb cards and higher can be sketchy ...
Best suggestion is 32gb and lower...
class 4 sdhc cards
you can use higher classes..
but the sweet spot is class 4 ...
the speed of higher can be problematic depending on your usage of it on your NIT