re: I want to try a Fallout game on the PC, should I get 3 or New Vegas?

Fallout 3. Capital Wasteland >>> Boring-arse desert. Gameplay isn't that different, especially given their ages at this point, and FO3 has some amazing mods to update it as well. It's an entirely more atmospheric, fascinating world to explore.

To this day, my memories of originally playing through Fallout 3 are so vivid that it almost feels like the Capital Wasteland is a real place that I went and visited.

I put such an emphasis on atmosphere because, let's face it, neither game is going to pull you in because of a strong plot, well-developed characters, or amazing game play. That's the downside to open-world games. With that said, I do prefer the story, characters, and quests in FO3 to New Vegas as well.