I think if you want a meaningful story, Fallout 3 is the place to go. However New vegas offers better gameplay and more features. It's to bad there isnt a "Both Are Pretty Good" option to vote on.

A few simple mods can make Fallout 3 better than NV or at least on the same level.
So I pick fallout 3

I like both in different ways, but I must say that vanilla I prefer Fallout New Vegas due to gameplay changes it has over Fallout 3.
I love the underground in Fallout 3, sewers and Metro tunnels are just great to explore, but as I already mentioned the gameplay is much more to my taste in Fallout New Vegas.

I like them both equally for different reasons.

I love the exploration and large world map of Fallout 3, the design over all is much much better than new vegas and is much more interesting on the whole. Mods can make it more like NV but fall flat gameplay wise I think. There are some amazing mods for Fallout 3, but there are better ones for NV in my honest opinion just because it is more mature modding scene coming over from Fallout 3. New Vegas has waaaaay more interesting NPC's and quests. Fallout 3 falls completely flat here, as do most beth games. They create awesome worlds but they really need to hire better writers and quest designers. The mechanics in NV are better too, but the diversity and design of areas falls flat compared to Fallout 3. However mods can make up for this in large part and really do shine in New Vegas much better.

All that said, I can just play TTW and have the best of both worlds.

@Roy Batty wrote:

I like them both equally for different reasons.

I love the exploration and large world map of Fallout 3, the design over all is much much better than new vegas and is much more interesting on the whole. Mods can make it more like NV but fall flat gameplay wise I think. There are some amazing mods for Fallout 3, but there are better ones for NV in my honest opinion just because it is more mature modding scene coming over from Fallout 3. New Vegas has waaaaay more interesting NPC's and quests. Fallout 3 falls completely flat here, as do most beth games. They create awesome worlds but they really need to hire better writers and quest designers. The mechanics in NV are better too, but the diversity and design of areas falls flat compared to Fallout 3. However mods can make up for this in large part and really do shine in New Vegas much better.

All that said, I can just play TTW and have the best of both worlds.

Completely agree re: emptiness. I also find that I need to put a flora mod on when I play. Chernobyl shows that trees don't die from intense fallout, and I always loved the look of abandoned cities that have been reclaimed by nature. It's also kin of ridiculous to think all these people survive on 200 yr old canned food without growing anything new. The main quest still makes sense about providing safe drinking water een if the landscape is already green. The only bit that doesn't really make sense is the Oasis quests, but they have a guy who's turned into a tree in them anyway so they were never going to make sense.