On a team with Brunson entrenched as the starter, Grimes is the most ideal choice on our roster.
He’s the incumbent, has the best size, and his trajectory is on the way up. He’s tue best fit with a traditional lineup.
Quickley may be a better, more versatile player, but his style of play and ability to play a legit PG makes him a great change of pace player. If you put him in with Brunson you become a faster team and Brunson’s own play becomes less predictable - at the expense of losing some size/strength/wing defensive flexibility (you’d be outsized by most starting backcourts). If you play him at PG, he brings a lot of the same as Brunson - and probably better defense.
Of course, it also depends on what happens at SF. Grimes makes the most sense of RJ is the starting SF. The Knicks could also go with Josh Hart as the starting SF (unlikely) - he does all sorts of good things, primarily if the game plan is to get Brunson and Randle off to good starts. Hart’s X-factor was really around his 3pt shot. He shot well over 50% from downtown as a Knick and I believe also on the WC team. Maybe there’s some permanent tweak he’s made.