If you think 12M is going to be the best MOS for you, you need to look at the USAR.
I've never met a Regular Army 12M, but I've known dozens in the Reserve. You will of course be limited to what is in your area, and they are not the most common of units (I could tell you about Kansas, but not Texas off the top of my head)
Houston FD has its requirements published online. I doubt 12M meets the certified firefighter/EMT criteria. 68W might, but I don't know enough about the terminology. If it doesn't, 68W might not be any more useful to you than 11B.
If the MOS isn't going to help you on the certification, I often recommend 74D as a resume enhancer for emergency management positions.