Congrats on your interest in skilled trades!
The term " good pay" is relative. Would you be better off with $40,000 in San Antonio or $65,000 in San Francisco? Please learn two things as you start out in life:
1. about Cost of Living Calculators - they will help you compare two different locations to get a better perspective. You will need more than twice as much to live in San Francisco! https://www.nerdwallet.com/cost-of-living-calculator/compare/san-antonio-tx-vs-san-francisco-ca
2. Managing money -learning to live below your means, creating an emergency fund so you don't have to run up a balance on credit cards, etc. You don't learn personal finance all at once. It's a struggle, lots of trials and errors. The key is to keep the errors to a minimum!
Also, if you leave friends and family behind, there will likely be some traveling back and forth to factor in.
I don't know if there's a best place to be a mechanic. I don't know of too many garages that are heated and cooled, so I'd want to work somewhere with tropical weather. Honolulu? Oops, same cost of living as San Francisco! You get the idea. . .
I'd like you to consider aircraft mechanic. Lots to learn, but, earning potential is awesome! And for either car or plane mechanic, consider joining the military for a few years to get off to a good start.
Best of luck!