Personally, I would say Grookey will be the one. Of all the Pokemon Ash have, Water types are the most abundant type, so I think Ash can skip Sooble. Then again, the main characters always have the three starters of the new region; so, even although he shouldn't have it, Ash will get Sooble, along with Grookey. We will have to wait until we see all the Pokemon in this Generation, to see which new Fire Type suits Ash better.