I want to re-enlist in the Army. What MOS should I pursue?

I recommend you to go talk with a recruiter to at least find out if the jobs you want to pursue are even an option for you. If they are, chose the one you have the most passion for not the one that’ll help you fast track. In order to benefit, thrive, and be fulfilled, you must pick/select a career field that’s dear to you. Good luck to you...

You need to go to a recruiter. You will need to find out what kinds of units are in your area and if those units have slots available. Most units require at least 1 68W, so you may have more luck there. What you don't want to do is get yourself stuck on a certain MOS goal just to find out that there are no units with that MOS near you. Having said that, if you are not tied down, an option may be to relocate to a region that as the MOS and slots you desire.

Both are good fields to pursue.

31B helps prepare you for physical security, personal security, non (or less) lethal training and similar civilian positions. It can also prepare you for similar cross fields like 31D CID if you have the degree & are able to meet the other requirements. https://www.youtube.com/watch?v=GX3_cRkbdWQ

68W on the other hand would prepare you for something in the realm of paramedics on the civilian side. https://www.youtube.com/watch?v=9PdimHHqJ-4&t=13s

Also consider the travel distance from your home to the unit's location.

*Note* These videos are geared more towards active duty, but should have relevant information either way.