I think FO3 and FO:NV are both quality games. It's not entirely fair to say one in better than the other because each offers something the other doesn't have. FO3 feels more like a FO game, to me. The abudance of super mutants, the wrecked and destroyed infrastructure, the feeling of living on the cusp of survival. FO:NV is brighter, the atomic bombs haven't levelled everything, there is more stuff (outfits, guns, ammo types, gun mods, enemies), and it really comes down to how you enjoy the FO experience.
As for FO4, it seems too early to speculate too much. I hope to see a remnant Enclave army, preferrably an Enclave faction you can join, as the evil factions are decidedly lacking in the FO series. There could be an NCR West vs Brotherhood East showdown, but I see that as the setting for FO5, there is still a ton of story that they can lay down before a confrontation between the two super groups.
Also, because Bethesda love to rehash old ideas, I would not be surprised if in FO4 you start the game in some sort of penal colony or in a retro-future jail. This would be a throw back to Interplay's FO3 idea, and also to Morrowind-Oblivion-Skyrim, and if there is one thing Bethesda can nail, it is starting out the game as a prisoner/outcast.