I'd go for the Benjamin Discovery, remember with the PCP air rifle he'll either need a hand pump (comes with Discovery at under $400 but not with the Maurauder) or an air tank capable of holding high pressure air (usually at least 3K and a source to fill) The Discovery is an excellent air rifle that is insanely accurate. I consistently shoot groups at 25 yds that you can cover with a dime using mine, I also have a RWS 34 spring gun but haven't shot it since I got my Discovery. I started with the hand pump that comes with the rifle and it's fairly easy to use, depending on how big your son is you may need to help him top it off for the full 2k psi fills...the nice part is after it's filled you can shoot 20+ shots without needing to pump it up again.
In accuracy the pcp is the way to go, springers aren't going to beat it in all but the rarest of cases. I don't see many guys shooting springers at 50 yds or more but I do my Discovery all the time with amazing results.
