The M1 visa has some advantages over a J1. For example, you can extend an M1 several times (not sure if there is even an upper limit) and remain in the USA whilst doing so. Working on it is possible, but only at the school where you did your training (your M1 visa sponsor). I did know someone who had extended his M1 for at least 4 years!
The J1 is valid for 24 months maximum and usually cannot be extended unless you are going to get additional work experience from the sponsor, for example, working in flight management etc. Even then, I believe it's limited to 6 months max. However, you can work anywhere on it.