Should I play with a pick or my fingers?
Ultimately you should be comfortable doing either one. A lot of people switch over to bass after playing guitar with a pick for some time. Unfortunately many are too lazy to learn to play with their fingers. That's not to say all pick players are lazy. Some styles of music sound more correct when played with a pick.
I prefer using my fingers to a pick. I feel l have far more control and I like the feel of making contact with the strings. You get a bassier, fatter tone with your fingers versus the thinner, scratchier sound of a pick. Although for a lot of faster, more aggressive styles sound better with a pick. The tone you get will depend on the type of pick and your picking technique too.
The short answer is choose the tone you want from your bass and practice the technique that yields that tone. Don't just choose what's easiest. In music, the path of least resistance rarely takes you to greatness.