I found New Vegas to be somewhat boring, and not feeling the post-apocalyptic feeling I had in Fallout 3.
I agree, I preferred 3 as well.
I have to agree with this. Fallout 3 felt MUCH more post-apocalyptic than New Vegas. There was simply too much civilization in New Vegas.
I'd suggest playing both, but this is the main difference between the two.
Fallout 3 is more post-apocalyptic, and New Vegas is more post-post-apocalyptic.
Fallout 3 has a pretty lame story in my opinion, but it's a hell of a lot of fun to explore the wide-open wasteland. That's the part that I think is the biggest reason some people prefer Fallout 3.
Fallout NV on the other hand feels as though you can't go too far in any direction without hitting some kind of civilization. For that reason it does lose the allure of having a giant empty world to explore. However, the storyline is a lot better, and it's more shades of gray than obvious good vs. obvious bad ending.