Get the kit versions if you can, RTR usually works out more expensive in the long run.
They are both good though, the ST is a bit more solid (IMO) and parts are cheaper but the Matrix comes with a better radio, the engines are about the same in both truggies, SH vs Mach .28's. both good.
My brief pros/cons

Hyper Pros
-cheap/plentiful parts
-solid
-dialed out of the box
-good steering servo

Cons
-plastic shock towers (strong but..)
-needs better chassis bracing
-crap battery holder
-Diffs are a bit tricky to get at (fixed on the Pro)
-cheap AM radio
-weak throttle/brake servo

Cen Pro's
-looks cool
-decent FM radio
-nice layout
-SH .28 power, although pullstart
-strong 23mm hubs

Cons
-23mm wheels are a PITA to buy/find
-cheap alloy knuckles break easily
-bellcrank is flimsy
-parts not so common and a bit more pricey

(yes I've driven both and have owned Hobao/Cen products)