1) Both are fun, but its more of a perspective view. U must try both out to see which one u're more comfortable with.
2) There is no which is better instrument, but a general view is Bass seems to carry more presence cos certain bands don't really need a guitar, i've seen bands that consists of Keyboard, Drums and bass. No guitars at all. An Example is Niacin.
But well, it depends on the type of music u play.
3) Bass is the heartbeat and the foundation of the music. It works closely with the drums. It gives the groove and the vibes.
Guitar on the other hand, gives variety and colours to the music. Cos u have diff strummming, picking, solos, chords. So its beatifies the whole music.
4) Mostly Guitarist can also learn to play the bass easily or vice versa. So there's no restriction that once u play guitar, u can't play the bass or otherwise.
Most imptly is u enjoy wat u are playing. That's wat it matters.
Cheers! Peace