What’s the best MOS in the military to get out and start making good money right away?

Honestly, very few, if any. While the military MOSs may give you the experience and training to step into another role as a civilian, the single most common theme/recommendation from civilian recruiters is that you have to invest in yourself after you transition. The Army presents the opportunities to step into these roles but you still have to invest in the civilian certifications to be competitive with your peers. Here's an example: a good friend worked as a 25B in SFG. He was trained on all the new equipment and was offered a job by the civilian contracting agency that worked on their networks there. But when he separated he couldn't get hired. He had the experience, he was far more technically proficient, he was even the preferred candidate. But he hadn't finished his Sec+ and CompTia certification before separation. Most MOSs will give you enough training and experience in a field to get certified, but very few Soldiers will bother to get the certifications because they believe their experience, or being a Veteran, will make them more competitive.
The monetary value of your military job is equal to the value of your civilian certification.

Doctor, Physician Assistant, or Nurse.

I'm currently in the job market and I've noticed a lot of job listings seeking military vets with any type of electrical or electronic experience. Especially companies that specialize in fiber optic, semi-conductor pumps or testing, installation of clean room equipment, just to name a few. Many of these positions are technician or installer jobs that don't require degrees, you just need to know basic electronic fundamentals, and know how to use testing equipment like voltmeters, multimeters, and oscilloscopes. PDB soldering/ welding is a plus. Starting pay in Oregon and Washington is around $20 to $25 DOE with bonus incentives for shift differentials. That's almost double the state minimum wage. I've met former navy techs and marine mechanics who went this route instead of college and are happy with it. Some have progressed into management/supervisor roles.

I've also met a vet that was a data analyst who went to a coding boot camp (Epicodus?) for $8,500 that included an internship and was able to get short term gigs that paid $30+/hr. So, even if you don't have the best MOS you can still find training that only takes a few months. Amazon also has some free cloud management training to supplement your free cyber training at FedVTE.

That's pretty much the trend I see in my area: electronics, coding and anything cloud-related (including business intelligence). However, there really is no shortcut to success unless you're really good at professional sports, acting, or singing.