Stovetop only because it allows the grains to cook longer and soften up and they end up absorbing more water. Plus, its easier to control the consistency on the stove. My only issue with this method is that if you dont know how to prepare cream of wheat on the stove, you end up with these lumps.
Its only the dryness of the cream of wheat I worry about when I prepare it in a microwave, the stove top is the most sufficient way to prepare the dish cream of wheat, when it is prepared in a microwave it is never to even compare to thou of stovetop cream of wheat, the only proper time I prepare it in a microwave is when I am feeling sloth (ish), other times it is going to be stove top