well, i played through fallout new vegas twice, and i still love it.
i got fallout 3 a few weeks ago, and i am still playing through it.
i liked new vegas more because you have more freedom choosing what faction you want to join, unlike fallout 3. (well i don't think you can choose a faction in fallout 3. correct me if i am wrong)
but fallout 3 has better atmosphere, and mostly a better map in my opinion.