Should I start by playing guitar or bass?

OK, so I'm going to put my birthday money toward a guitar. I'm not very musically talented, but I am taking a year off and want to learn the basics of music.

I know I would want to play the guitar much more than the piano. I never could work up the discipline to practice/play keyboard when I tried as a kid.

I'm going to try to teach myself some music theory by using Garage Band or something like it (recommend anything?)

So I want to know whether I should choose guitar or bass.

I am very new to music entirely.

Should I just stick to fucking around on software?