Fallout 3 is my favourite game. Fallout new vegas is definitely not my favourite game...

fallout 3 hands down

Their all good in my opinion but Fallout 3 is better for it's story and it looks more post apocalyptic but on the other hand Fallout is more of a fun game and it does look very very nice with the desert but you don't get that post apocalyptic feeling to be honest.
I love both games and there is endless hours between them but get Fallout 3 if you have never played a Fallout before

I would recommend buying FO3 first.
I loved that game but for me, I couldn't play it after I beat New Vegas. The feeling of NV makes the game have a whole end of the world feeling that I love while FO3 is a lot happier and brighter.

I think FO3 was better anyway, but New Vegas is pretty good but the replay-ability is low.

Fallout 3, it just feels so much better. The darker atmosphere is also a plus.

New Vegas is much better.
-better storyline (which has continuity with Fo1/2/Tactics, contrary to Fo3)
-better quests
-many more quests on top of that
-better soundtrack, and definitely better radio
-better, even if smaller, map

And a lot more stuff, which are much less noticeable (non-combat problem resolution being much more frequently possible, for instance).

Fallout 3, just because it felt more wastelandish, and also exploring seemed to be more rewarding and it felt like there were more secrets to find than NV. Either way Fallout is easily one of the best single player games to date.

It's all on preference my friend, but in my opinion it's defiantly fallout 3! Don't get me wrong they're both amazing games but fallout 3 has a better story but is really buggy. Fallout NV has great companions but quite a shi*ty story line compared to fallout 3.

Fallout 3 had the best story and dlc. 'nuff said