I'd have to say overall Fabric.com because I've never gotten a poor quality fabric there, prices are reasonable, and shipping is FAST.
Hancocks of Paducah is *good* but the ship time is LOOOOOONG. Huge selection. Good prices. Sales are great. Their ordering system is not very clear, and the last couple orders I thought I "got" several fabrics, only to find out a week later that "backorder" really means "cancelled".
One I found from here was Quilt Fabric Closeouts. Great prices, great quality. The package was packed with such care, it was BEAUTIFUL. Like, they really care about their fabric there.
I did the free deal thing from Missouri Star Quilt Co, and I think I'll have to shop them more often. There's something really, really good about these folks. I just can't quite put my finger on it. It's the personable nature that gets me, I think. :D