Well, I have both, but my first one was Pokemon White, simply because I love electric types, and than you could catch Emolga! I never really ended up using it a lot, anyways, after I've played it twice, I really started to love Reshiram, it looked so much cooler than Zekrom, so there I was, a week after I bought Pokemon White, They probably thought I was a nerd :P. Anyways, so I played Pokemon Black, and I loved it. Pokemon Black is my favorite, Simply because I love Reshiram, I never use legendaries tho, so I just used it once, to fight against N. But Pokemon Black still won.
But I liked Opelucid City more in Pokemon White, because it wasn't so modern. =P.
And White Forest was more fun for me, just because it was so peacefull.