Neither is perfect, but I prefer dealing with B&H if they have what I need.
I really appreciate the accurate, up-to-the-minute stock information at B&H, and for the most part I've gotten good service from them. The worst experience I've ever had with B&H was ordering a 5L bottle of Ilford Hypam along with a bunch of lighter, more fragile darkroom stuff. I'll think twice about doing that again - they tossed the whole mess into a flimsy box with grossly inadequate filler. The box arrived mostly shredded; it was amazing none of the contents was missing or damaged. A minor peeve is that recently they've started sticking big, obnoxious bar code stickers on the merchanidise you order; if you like keeping your precious jewel in a pristine manufacturer-issue box you can forget it.
My experience with Adorama is mostly limited to used merchandise. I've gotten some good deals, but you have to pay close attention and ask questions if anything seems the slightest bit odd, because they seem to have a relatively high rate of misidentified items. It doesn't appear to be intentional, because it's not systematically in a direction that jacks up the price or makes more money for them. Rather, it just looks like plain old sloppiness.