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.
Personally I prefer the bass. It's more consistent musically than the guitar, common in more genres, and it's great to learn the mechanics of intervals and the role the bass has. With the guitar you have that stupid smaller interval between G and B...which does make doing chords easier, but it screws with your intuition. Basically, if you want to make music more easily and go to open mic night and screw around, the guitar is great. If you think you're ready to really dig into the meaty theory, you want to play with other musicians, and you don't mind not being able to just strum your troubles away, go for the bass.
I must disagree with >>2's thoughtful comment. The bass is a rhythm section instrument and almost always played as such. If you want to learn about how different Intervals interact to form chords go with a the guitar.
Although they are very similar, they are played very differently; the guitar plays a similar role as a keyboard, while the bass in practice is more similar to the drums than the guitar.
Really, I suggest that you play around with a guitar, and also play around with a bass, and see which you prefer. I have a guitar and a (short scale neck) bass.
As the time has gone by, I've found that I prefer to play with the bass.