That depends on which part of the song you enjoy playing. The bass typically plucks one low note at a time, driving the rhythm of the music. The bass player doesn't play the melody. Guitar players are often Fronts in the band and play melodic and harmonic chords and the melody line. Both will take practice.
A lot depends on what your band needs and what you are good at. The guitar is more versatile, has more use across a wide range of musical genres, and can function as both a solo and rhythm instrument. The bass is usually (but not always) strictly rhythm.
The decision is entirely up to you. Both are stringed instruments, and are similar, however the technique to play them is different. Why not play both?