Eh. A lot of the mechanics of new vegas we superior, but as a whole I still prefer fallout 3. It comes down to the setting in DC. It feels so much more like a nuclear wasteland, and some of the encounters turn out far more epic than new vegas.
I enjoy Fallout 3 over New Vegas; post-apocalyptic DC grabbed me more than the Mojave, and it doesn't have nearly as much horrendous backtracking through the same areas that New Vegas does (through the stip, everywhere else is fine).
Sure, the plot is more open-ended in NV, but they're both pretty average anyway. I play those games for the attachment to the characters themselves and the world they interact in, and Fallout 3 is more enjoyable for that.
A better game than what?
If you are talking about all of the Fallout games, then yes, it is better than Fallout 1, 2, and the spinoffs. Fallout 3 is the best Fallout game though.
They're both good games in my opinion, I like New Vegas more because of Veronica. Together we went around punching everything into the ground, Fallout 3 was different Fawkes had god mode always on and did massive damage and just would not die to any enemy which was really funny to watch.