I agree with B on that, considering this topic has been covered so much.
However, because I know how annoying it is to go off and search, I'll give my input.
I know Louden Swain swears by inclined presses. They don't stress the upper-pec moreso, but they take stress off of the lower-portion of the pectoral region. Dumbbells are probably a better mass builder because there's no bar which stops you from bringing the weights down further, thus giving you a greater ROM.
The main reason I feel however, that the dumbbell stresses the chest more, is because it causes them to act on their own. No support from the other arm or opposite half of the chest. They must stabilize themselves. It's much harder to control dumbbells than barbells. I've yet to meet anyone who says otherwise. As for actually building mass, so long as you train the chest, and eat big you'll get big.
I agree with the idea of switching it up. Get the best of both worlds.
And by the by, do what your body tells you. If you feel more stress in the pecs with dumbbells, then use them! Apparently they're being targeted more. And muscles grow when the fibers are stimulated, when there's enough fuel for them to grow, and of course when you're sleeping. They're all linked. Can't have one without the other.