I would like to qualify my answer a bit more.
I think Ben Simmons will have the more high profile numbers and will likely be the bigger star but I think Ingram will be the player who be more conductive to winning and contending just because shooting is so valuable and I think he will prove to be the better defensive player long term.
I just have real questions about Ben Simmons being able to shoot the basketball well enough to play on the perimeter where I think he has a much better chance to be a quality defender. If he ends up playing as a PF I just don't think he will be conductive to having a good defense. If he develops a quality jump shot and three point range I think his length, athletic ability and rebounding will allow him to be a defensive terror at times especially with his ability to ignite the fast break off rebounds or steals or blocks.
If he lines up as a pure PF though I don't think he is really physical enough to hold his ground in the post or defend the paint in general from the strong side. Flying in from the weakside as a help defender and or grabbing rebounds out of his zone or dropping down to blitz a post up threat.
I think bulking up to handle doing the dirty work and taking the pounding at PF would be counter productive and take away from what makes him a special prospect as I think its too risky that bulking up would limit his ability to glide around the court.
Ingram is much easier to project as to what he is going to be with the only real question mark being how much he will fill out physically (my best guess being that he spends most of his career in the 6'9 215-220 lbs range after he fills out sometime early in his second contract.
His length, size, basketball IQ, work ethic, foot work and under rated athletic ability will allow him to be a quality defender even before he fills out and once he does fill out he will likely be just as underrated defensively as Durant has been.
Offensively with his length, size, high release point, foot work, feel for the game will allow him much like Durant and Nowitzki to get off a quality shot against nearly any defender at will. The limit to his ceiling offensively will be tied to his ability to create shots for others at volume like Durant or if instead goes the Nowitzki route where he will just be an insanely efficient scorer/shooter whom almost never makes negative plays?
Ideally he would split the difference as I don't think he has it in him to handle the usage load that Durant is able to as a guy that can take 20 shots per game while averaging 5 assists but at 3.5 turnovers he is forcing it often (though I think its a product of frustration from having to play with Westbrook and that his assist numbers will climb or at least his turnovers will dip dramatically now). My projection for Ingram's ceiling would be in the range of 24 PPG, 7 RPG, 3+ APG, 1 SPG, 1 BPG while keeping his TS% in the elite .565 or better and keeping his turnover in the low 2's.
