They're 2 different games lol
But Audiosurf 2!! Because who wouldn't want to play a game that's synchronized with the beats of your own music? Rise of Triad can wait :3

Diet Sprite or Vodka?

Audiosurf2 theoretically will give you a gameplay time represented by the formula:

(Music collection total time x number of modes that you will play x the number of people that will dethrone your high score) divided by your average ranking in audiosurf 2 leaderboards

So it will be more economical to get audiosurf 2

Audiosurf 2
Audiosurf 2
Audiosurf 2
Audiosurf 2
Audiosurf 2
Audiosurf 2
Audiosurf 2
Audiosurf 2

Just to be that guy. Rise of the Triad.

Audiosurf 2

Its hard to tell you which of two completely different games you'd enjoy without you telling us anything about what you're looking for in a game in the first place. I'd personally go with Audiosurf 2 because I like to use it as an interactive visualizer, and because its just fun in general. I haven't played Rise of the Triad but Audiosurf never got old (since I have a huge and varied music library) and this new one has even shinier gameplay so I'd go with that.

I have a lot of fun with Rise of the Triad. Nice lengthy campaign, good graphics, nice humor and a lot developer support. (Map editor and Workshop support soon). Also the multiplayer is very nice and satisfying.

Well, if you've played the first audiosurf, I would say go for the other game as it will be something different/new. I mean, how much different can audiosurf 2 be from the first one? You can always buy it later and it's not like you don't know what it's going to be like.

Its like making a choice between an apple or a potato. They are both completely different game.