I wanted to play bass, but couldn't get my folks to buy me one, so while I was saving up to get a bass, I used my sister's acoustic guitar to work out bass lines. As a side line, I worked out some chord shapes by ear, the major, minor and dom7 on the top 4 strings. Eventually I bought a chord book, so I could extend what I was already using to full barre versions. I didn't use much of the 1st position 'campfire chords' because I was learning tunes from the record, and barre chords were easier to use for that. It was all early Stones, and similar bands, 12 bars Cuck Berry style. It wasn't until the Yardbirds, with Clapton & Beck, that I wanted to play solos etc. The there was the problem of getting the Clapton/Beck sounds with no info on how. ATT I was playing bass, acoustic guitar & blues harp, but manged to buy solid guitar and got the sound by using the banjo 1st trick, and plugging into the mic socket of a valve tape recorder.
From my experience I'd tend to recommend trying a short scale (30") bass first (if you can find one!). I think guitars are relatively hard to start with. With bass you only need to finger one note at a time, the lines can be be simpler but stiff effective and you can probably join a band quicker than getting proficient on guitar. Obviously if you're looking for singing accompaniment, or solo line guitar then bass is less useful, but I think it's a good option, especially if you don't progress well on guitar.
