The consensus in the media seems to be Fultz. He does look like a very special player and I would personally consider him the top choice. I really can't make the argument for anyone else over him.
I think one way of looking at it is this...
Who is going to lead the NEXT era of Celtics? Once guys like IT, Al, etc hit their peak years?
It seems that Jaylen is in that group. The 2018 draft is loaded with bigs, so there is a good chance we could get a key piece for the future in that draft, and then you have Fultz.
We could be building our future core with Fultz, a top guard prospect, Brown, a top wing prospect, and a top big prospect from next years draft.
I trust Danny and co. to look at the players and decide, but I think Fultz is the clear choice as of right now.