I always prefer RPMs. Not because I dislike PL,no I love them, but they should stay with what they do best..creating rubber parts (tires!) and I too love PL's body designs for the Slash.
The reason I would never go with PL skiplate is..just look at that sharp angle on the rear one..that would cause the chassis to kick up when bottoming out over rough terrain. But kudos to PL, for creating an integrated bumper mount! That's a good innovative idea, rather than buying separate parts like RPM.
Take a look at RPM's design,
http://www.rpmrcproducts.com/products/traxxas/hires/81246.htm
it's much smoother and has more rounded transition angles, this will minimize kick up. I currently use the RPM skidplates..so far they live up to the manufacturer's claim..they're that good!