He is a better passer, better at retaining the ball, better vision, more tenacious and tries to get stuck in more despite his size. KDB is clearly better in front of goal and has more pace and stamina.
A fit Silva is the better player IMO (not the Silva of most of this season). The difficulty is in keeping him fit.
Anyway It will be interesting to see what Guardiola comes up with in terms of formation and player selection. I'm hoping those that stay get a clean slate and the chance to show what they can do under his leadership along with 5 or 6 new faces.