Fallout 3 or fallout new Vegas

Fallout New Vegas is LITERALLY an upgrade from Fallout 3 other than setting, storyline, and characters except the characters are way deeper since, y'know, there's lots of references and cameos.

Simple way to enjoyment: Buy both, Install Tale of Two Wastelands and make a complete run from the Capital Wastelands to Nevada.
If you don't know what Tale of Two Wastelands is: It merges 3 and NV together in NV engine, with all the mechanics NV has to offer.
Just needs the complete (international) GOTY/Ultimate Versions.
Although not many mods work for TTW, WMX is there for it and is highly recommended.

Buy both but play Fallout 3 first to get the basic feel.

I'll put it to you this:

View attached image.

Fallout New Vegas >>>Fallout 3

New Vegas have better quest and story.
It's more RPG.

What everyone else has said. My vote is if you had to choose one over the other, go with FNV. It is the better of the engines and has more fleshed out story lines...

However, you can play Fallout 3 and ALL DLC inside the Fallout NV game engine with the mod www.taleoftwowastelands.com. This gets around the Windows compatibility issue too. TTW mod allows you to take your Fallout 3 Goty install and treat it as DLC withing Fallout New Vegas. Its a complex mod, but it is good to know you can play through Fallout 3 this way.

new vegas was a much better experience for me, the map, enemies, leveling and system (skills, perks, requirements, lockpick/hacking) felt much less annoying than in fallout 3. it also lacks those useless dungeons they loved to put in morrowind/oblivion/fallout 3 where you went 5 levels underground just to find a sack with 3 bottlecaps -_-
i might add that NV is also less forgiving.

if you want to play them all, you should pick fallout 3 first, if not, just go directly to new vegas.

Fallout 3, felt more "at home" in the Capital Wasteland.

In fallout 3 you can create weapon that uses teddybears as ammo. You can't do this in NV :(

Fallout 3 .

Both.

Fallout NV GOTY

New Vegas is far better. New Vegas got right everything that 3 screwed up. Awesome story, vibrant setting, actually interesting "villain". If you liked the new Mad Max (or any of them really) then you'll feel right at home in New Vegas. The only part of 3 that I really liked was the DLC "Broken Steel."

had 1000G on xbox for both of them, but i prefer Vegas.

New Vegas, easly. Much better game.

I prefer Fallout New Vegas, but if you are new to the games, I would choose Fallout 3