I prefer Fallout 3 but because it's the exploration I love about these kind of games and the Fallout 3 environment had more landmarks, more obscure unimportant locations that still had its own small interesting story to discover.
F:NV did, however, crush Fallout 3 in the line of a coherent story. If you took the time to analyze Fallout 3, it reveals a lot of plot holes.

Functions and mechanics are better in New Vegas, but the feeling and the theme in FO3 is superior in my opinion.

I think most people hated how New Vegas was poorly made. For me,I had built my computer specifically to handle New Vegas with the best texture pack mods and I built it to handle anything New Vegas could throw at it.

Guess what? I bought mine on launch,and it ran like shit. I couldn't even get it to run correctly,micro stuttering jaggy lines,and long range texture flickering. Even after mods such as the New Vegas Error Corrections and the micro stutter removers,it still would run like crap.

After 120+ mods I finally got it to run stable-ish. I liked the game,but I hated the Mojaves enviroment. Wandering about in the desert was alright,but it got boring when I fought more deathclaws than people.

Then you never went to where they usually hang around. The fastest route to Vegas takes you though the Death Claws.

If they Claws didnt fuck you up the Cazadores would.

And I *hated* how the Raiders had so much energy weapons.