Andy actually has a great series of pages on this very topic.
http://www.zdspb.com/tech/misc/solenoids_design.html
http://www.zdspb.com/tech/misc/solenoids_models.html
http://www.zdspb.com/tech/misc/solen...tactuated.html
http://www.zdspb.com/tech/misc/solenoids_humphrey.html
http://www.zdspb.com/tech/misc/solenoids_mac.html
http://www.zdspb.com/tech/misc/solenoids_smc.html
To (painfully breifly) answer your questions, SMC, Parker and Humphrey solenoids used in paintball are indirect acting, whereas MAC valves are direct acting. Direct acting is typically a faster response. Humphrey developed the CRCB series of solenoids to be more resilient at higher pressures, but the tradeoff is a somewhat slower valve than the "equivalent" Parker.
As an aside, PE did use SMC valves in some older Egos, but in their high-end markers they use custom MAC valves now. I think they might still use SMC valves in the Etek, maybe even a clippard valve in the Etha. I know Clippard has their valves manufactured in Italy, at any rate.