Shape?
Material, carbon fiber, graphite, fiber glass?
Weight?
Type of sling attachments?
Placement of sling swivels?
Placement of Bipod attachment?
Adjustable cheek rest?
Adjustable LOP?
Other Features?
MPA competition chassis is really starting to dominate in our neck of the woods. I would say out of the 10 best PRS shooters I know in our region, probably 7-8 of them are shooting MPA chassis systems.
Heavier is good, helps recoil mitigation, plus a heavy chassis balances out a heavy barrel.
Sling stuff doesn't really matter for PRS. A couple flush cup attachments are all you need.
Full length Arca Swiss rail cut on the MPA is awesome, interfaces with a tripod if needed, but even more handy is the ability to slide your bipod fore/aft. Putting the bipod near the magwell and putting a bag under the hand grip is almost like shooting prone, even on a very small surface or odd object.
Adjustable LOP and cheek rest are pretty common on most chassis, MPA has that.
MPA's barricade wedge block is very handy and works well in the right situation.
Fore-end of the chassis is nice and square/flat so it rides the bag well to help tracking on recoil.
The vertical grip with trigger finger stand-off for the MPA is very helpful in making proper trigger pulls.
I have an MPA Chassis and a traditional Manners T2A carbon fiber stock which is a fair bit lighter. I'm probably going to ditch the Manners for a second MPA chassis. I've shot with and practiced with both extensively, and I have a higher hit percentage with the MPA chassis.