What kind of a topic is it? Fallout NV makes huge improvements over Fallout 3 (weapon mods, ammunition types, repair benches, reloading benches, dehydration, hunger, sleep, better loot). But the thing is, both games are canon, and you cant say one game will be continued and other wont be. Both are part of the main story now. Gameplay wise, i'd definately go with F:NV minus the bugs and tiny map.