Three main things you need in M+ retail 8.2.5.

Interrupts on at least 3/5ths of the group and short cooldown interrupts.
High mobility specs like melee. You will be moving a lot. In some fights the entire time.
A lot, a lot of patience.

I would stay away from casters in general. If I had to do it over again I think my group would be all melee with 2 focused on trash and one focused on boss.

Also the dungeons are loaded to the gills with trash you don't need to kill in order to beat the timer. So utilities like shroud on rogues are essential.

Unholy DK has monster AoE damage. I was actually blown away at how good it was at 400 ilvl. So you could go that route, two unholy DKs and something like assassination rogue for boss killing. Pick your choice of tank and healer based on your own perceived needs.

For M0 you can run anything you like. None of what I said above applies in that scenario.