So far this season a couple trends are emerging at C position
Daniel Theis has been awesome defensively, leads the league in block %, and in general looks great switching onto smaller guys. He's still gonna get bulldozed by bigger guys. He has been okay rebounding the ball with a total rebound percentage of about 16% which would be something like 25th in the league. He hasn't provided a whole lot offensively shooting the ball as he's below 20% from 3 and below 40% from 2.
Robert Williams does some ice things like defensive rebound (over 20%), assist (over 15%) and block some shots, and provide some pressure on the rim in the form of rim running and lobs catching. He does some not so great things like turn the ball over too much, foul, and get out of position. But those mistakes are mistakes young guys often make, and I think can be ironed out in time. He deserves minutes, I think he will get them, he's a candidate to be the closing center full time by the end of the year.
Grant Williams is clearly a smart player, he is a pretty decent passer with the ability to hold his ground in the paint. He isnt nearly the rim protector that Theis or RW are, his rebound percentage of only 7.7% is very low for a big, he hasn't hit a three pointer yet and is pretty much a non factor offensively outside of 3 feet which is problematic for a guy who is 6'6. He looks like a rotation guy right now.
Kanter hasn't played enough for any sort of evaluation.
Poirer clearly isnt in the rotation right now, if he can't get minutes when Kanter is out dont see how he gets any going forward.
Smart is Smart, looks good defending bigger guys although when a guy gets deep post position they are able to just shoot over him. Having him play Center leaves you weak on the defensive rebounding. But he does give you the ability to go five out and space the floor with quick guys who can pass and defend at every position, and for some opponents thats gonna be the best bet.
If peoples opinion has changed feel free to change your vote.