Went with the last one as Fallout 3 was the only one I played
I heard a lot of the first two (including some highly religious speeches, descriptions and goading from a friend ages ago

) but I just never got into them. Sadly, I'm the type of player that finds it hard to go back and try most older games, simply because they can rarely live up to my expectations due to current-day games as competition.
Have to say though, F3 was one of the best games I've played to date. Awesome story (I found the beggining sequence an extremely awesome way to teach you the basic controls), interesting characters, great gameplay, vast landscape (I really love huge, non-linear landscapes) and a lot of replay value, not much more I could ask for in a game... only fault was a bit of a grave one, the fact they locked your gameplay after the final mission. Fortunately the DLC fixed that, but I'm torn between the opinions that either they were greedy bastards who wanted to sell their DLC or just amazingly incompetent/inconsiderate to put an "end" in such an open game to begin with.