Depends on your baby to be honest... boys tend to be larger than girls (but not ALWAYS).
My son was in NB clothing for 2-3 weeks - born at 7lbs 8oz.
I have some NB clothing for my daughter but have NO idea how big or small she will be so I didn't get too much. The majority of what I have in NB is primary colored sleepers that someone gave me for free... I didn't go and buy anything NB other than a "Little Sister" onesie that i got 2nd hand and a pink pair of NB pants to go with it that I paid maybe 10cents for considering they were in a bag of clothing i bought for $5. LOL....
In my hospital bag i have the Little Sister Onesie and NB pants and ALSO a 0-3 month outfit just to cover both scenarios for a take home outfit.