Kevin, if you fill out your profile we may be able to help you better. For example, do you own a bass or are you using the school's? If it's not your bass you might want to stick with something that's easy to put on/take off.
IMO the advice you've had here is very wide - ranging when you consider that Realist and String Charger are pretty much opposite ends of the spectrum. My suggestion, given your level of experience, is find something that works and then focus your attention on learning to play the instrument. Especially, but not limited to, acoustic sound production. You don't need to be spending your time buying and selling gear.
I'd have to recommend against a magnetic pu if organic is what you're going for. Bassmax may have the highest output, but it is less natural to my ears than Realist, being closer to the strings. A Realist might be muddy at big band volumes. So for your purposes right now, Bassmax or Underwood might be the easy choice. Of those two, Bassmax has more thump, which might be a good thing. It is also the least expensive of all pu's unless you want to make your own. Given all these considerations, I would say the Bassmax is the place to start. Rev Solo could be another option, but again not as hot a signal as Bassmax.
Whichever one you choose, make sure you get a good fit - snug and flush but not crammed in. You may have to file your bridge to achieve this. Let us know what you get and how you like it.