it all depends.. I was my mama's 1st and I was 2 weeks early.. perfectly healthy too.. 6 lbs. 10 oz! my brother (her 2nd) was born right around his due date she thinks.. and he was 6 lbs. 9 oz! every baby & every body is different.. I don't think it's "more common" for one or the other. (((:
I've always heard first babies come late. My due date was yesterday..... No sign of baby ;(
From what I've heard, first time babies tend to go later, after the due date... I was a first child and I was two weeks late. But my Mom didn't gain enough weight, so maybe that's why it took longer.