Alex! I can't believe you didnt tell me all of this (Or did I just miss you mentioning it) You know I was 8 years in the Marines, right? Congrats man and welcome to The Corps! Semper Fi!
As for which MOS to pick. Everyone has their personal preferences, and you have to realize that your choice will stick with you. Think about what you love to do. Do you like driving? Maybe Motor T would be a choice for you. It would help you getting your CDL in the civilian world. Do you like watching good guys take down bad guys on TV? Maybe then you would like to consider Military Police, where you can pretty much write your own ticket in the civilian world as a peace officer.
Do you see where I am heading with this? Look at the things you love to do. Remember that even though you may or may not make a life-long career in the marines, eventually that time will be up, and the civilian world will be ready for you. Anything that you can learn while in will help you in your future choices. Make a good one and let it help you. Personally I wanted to be a tank crewman. I was lucky enough that they didn't have any current slots available, and I ended up being a tank mechanic. And I LOVE working and fixing things. I learned a TON of things from my time in the Marines. This is something that you will NEVER forget. The Marines are the closest nit people I have ever met. We don't make friends in the Marines, we make life-long brothers. So consider your MOS wisely and think about your future as well as what is right in front of you. I would be more than happy to help you find more information. Welcome to your new family Alex!