I'd rather have Thornton.
After this season Thornton is a free agent. Jack is on the hook for at least two more with a team option for a third.
Next year MT becomes a nice, big expiring contract. And while Jack has been played at the 2 at times, if there's even a moment where he and IT are the backcourt for the Kings I'll be incredibly disappointed in the FO. Jarett Jack isn't a building piece going forward so why deal for him and be on the hook for his salary? The Kings should be looking to trim fat, not add it.
Jack can be a nice bench piece on a good team at a lower salary number. That's just not the situation the Kings are in and I don't see any positives that he would bring.
And what happened to the Kings looking to add a traditional pass first PG?