when you see a whole series and are deciding which one to get...

For video games, always get the "2"

For movies, always the first one is the best.

There are notable exceptions, though, actually i can think of a lot of sequels, movie sequels that are better than the original.

But with video games, almost always you want to get the second one. That's how games are, they improve. For the sequel, the developers put in all the stuff that they had to cut out to make the deadline on the first game.

Oftentimes, by the third in a aseries, the game is larded down with features, controls, super-moves(meta-controls) and and is overall less fun to play.