The biggest difference is the quality of the training products. FlightSafety has all the fancy PowerPoint animations, full colour training manuals, incomparable checklists, etc. The Simcom manual is nowhere near the quality of the FlightSafety one and their checklist is a throwaway item.
You are just as likely to receive a good or bad instructor at all of them. No difference in quality there.
Many of the Simcom king air simulators are not motion, but have better wraparound visuals than most motion sims. Unless you need motion to satisfy regs i would not say that one is any better than the other.
What you do want to make sure is that if you are going to a BE20 sim it is actually a BE20 sim and not a BE90 with the torque and temp gauges swapped out between sessions. Or vice versa.