that's a pretty interesting question. on one hand, any quilt block you like would do just fine. on the other hand, whichever block you choose is going to be covered up by the plate.
i think i'd be inclined to find a block i liked that would be easy to do in a very small size ... say 6" ...
form a rectangle by using a blank square of fabric in the middle, then two of each of the blocks (or 4 different ones) at the sides, one above the other. you could do a fancy quilted design on the blank square, or something simple since it's gonna have a plate covering all your work.
there are few blocks easier than the pinwheel so if you're worried about working so small, they'd make a good place to start. :-)