My issue with Clayton Jr. is that his limited size and athleticism make it difficult for him to get where he wants to go on the floor without the use of multiple screens. (I guess we'll see if the Jazz can create enough spacing for him when he plays with the regular rotation guys.) Collier is better than WCJ at breaking the paint, pressuring the rim and creating off the dribble. So it becomes a question of what style of play Will Hardy wants to use. The problem with Collier is that he has little-to-no value when he's off the ball. Until Collier shoots well enough to be respected, he can't really be your starting point guard long term.
I think that in the bigger picture, the Jazz are probably planning to build a team that can run a lot of their offense from the wing, or they'll use multiple creators, while the guy they play at the 1 will spend considerable time playing off the ball. This is what the Celtics did recently when they played through Tatum and had Derrick White and Jrue Holiday spacing the floor. WCJ fits that blueprint. (Keyonte does as well...if he'll play defense.) WCJ is potentially a knock-down shooter with deep range, who can also use his high skill level as a secondary playmaker.
In the immediate term, I think the starting PG is Collier's to lose. I think he'll be the starter to open the season. If Collier can get his 3pt shooting up to 34% or so, then people will begin to look at him as starting-caliber.