Hello and welcome to the dark side. As for mic vs. pick up that's a big question that you can read a lot about hear: AMPS & PICKUPS Links and FAQ: Please read before posting ("Newbie Links")
I don't know what a Puma 900 is, sounds like it might be an electric bass amp and not well suited for use with the double bass. Anyway, I would start with a pick up. Recommendations will be varied, many of us have found the pick up that works for our purposes.
Since you're new to the double bass I would suggest you spend some time with the instrument and not worry about amplification yet. Getting a good acoustic sound from the bass is the first step towards getting a good amplified sound.
Have fun with the bass!