What would be better for me to learn? Guitar or bass?

I've been a viola player for going on 4 years now, and i have taken an interest in the guitar and bass. Now my dad thinks that it would be easier for me to learn guitar first and then bass, but i think since a viola is similar to a bass and since i know 3 of the 4 strings already, i could learn bass fairly quickly. I'm worried that learning bass first will make it harder to learn guitar later on, but i would like to play both. If anyone could point me in the right direction for this, that would be great.