I owned both for years. Finally got around to playing 3, and really enjoyed it, especially the beginning. As the main plot went on, it got less interesting. Still, the wasteland was cool, and I liked being able to seeing "something" nearby or on the horizon; knowing I could walk there and check it out.

New Vegas, which I'm currently playing and loving, is the opposite. It starts so slowly that I had two mis-starts where I started the game, got bored, and quit. You can't see the next cool place because everything around you is blocked by rocks. But once you get started, and get into the game a few hours, the game is amazing. Mods make it even more so. I'm glad I gave it a third try.