Kenryoku_Maxis on 03 May 2009
If you're talking about just those three, I'd have to say SquareEnix. But honestly, SquareEnix has so little imput into Dragon Quest, I don't want to include them. Yuji Horii and his team (Armor Project) are pretty much a separate division of SE that get to do whatever they want because SE knows whatever they do, his games will sell.
And the people actually making the Dragon QUest games are people like Level-5, Arrtepiazza, Matrix, Chunsoft, etc.
Six upcoming games you should look into:
