They're both fine. I bought a used Honda Element that was already equipped with a Blue Ox baseplate so that was the decision maker for me.
I do like the fact that the Blue Ox system has one less step to hooking up - there's no crossbar to be connected to the car's baseplate. I think that the rubber boots that cover the sliding portion of the legs may help avoid water, grit and wear.
The baseplate that came with the car is BO's cheapest one - thetabs that connect to the towbar are not removable, so my Element doesn't look as sleek as it might (not that an Element EVER looks very sleek!). I double-checked with Blue Ox and they confirmed that it was one of theirs.
One advantage to the Roadmaster is that it affixes the safety cables to the towbar's arms. Blue Ox provides coiled cables. When you combine the coiled safety cables with the BO coiled electrical cable and a breakaway cable, it requires a bit of handling to untangle the mix when you're connecting or disconnecting.
Coyle & Sue
Cassity (Labrador) and Rylee (Standard Poodle)
2007 Damon Challenger 355; 2003 Element toad