Steel, Dragon, and Water are really easymode monotype teams. Fire's reasonably good now that you have defog. I was never sure on Ground's placement, I think it was good.
Monotype Ghost is probably good in Gen 6 due to being the new dragon.
Not sure how monofairy would fare actually. I feel like that would just be Azumarill, Togekiss, Mega Mawile, Klefki maybe, and then two filler.