What are good MOS's to transfer to civilian careers?

If you're looking for a Career, get rid of that mentality of "a job with skills that transfer".

Do you really think that after 20+ years you'll be for an entry level job with the entry level skills you picked up from your MOS? I hope you dream bigger than that.

After 20 years you'll need to get new certifications in whatever career field you choose. No matter what field you choose, you'll almost certainly need to take some classes to be on par with your civilian peers.

So, don't worry about what you'll do in 20 years, there's no way you'll know what you'll want to do by then. Just pick something you enjoy doing and can stand doing till you retire

51C is 100% transferable

Where does your subject expertise lie? What field do find most intriguing and challenging? That is your field.
You will find the most reward in a field where you can conquer challenges. If you are intrigued with the subject, the desire to find out all you can about it, besides, you will enjoy it; and that, my friend, is the deal maker.