Amici,
Either black or brown leather for me, with a snap, NO Velcro.. I can't remember how many times when I was in the field during winter training that the Velcro would get wet from snow and then all frozen up with the result of not being able to close the flap on your MT pouch. Also in the Spring it would also get occasionally gummed up with all kinds of gunk from crawling around or bushwacking through rough terrain and the problem would again result with a pouch that could not close.
I know that this isn't something that happens to the typical user using his MT to EDC or on his belt while hiking or backpacking, but it's something to think about.
Be it leather or nylon, as long as it's not Velcro, I won't give a "snap"..
Cheers,
Serge