I went with black cords on both of mine. Flat plugs would be handy, but the standard plugs are more authentic for an arcade cab.
Oh, no! When will the insanity stop. Now it can't have a flat plug because thats not arcade authentic. Good golly man its mame! How authentic is that?
Well to be truly authentic you'd need to tear out the ground lug with a pair of pliers, run over it with a dolly a few hundred times, ect...

The plug isn't a concern of mine though, all of the rest of my cabs have regular plugs, and I leave space between the cabs and the wall for air circulation. If the MAME cabs had flat plugs I'd still line them up with the others.