I believe the RBC has better options (I don't rmb if it's COLA, long term conversion at elderly age, etc). As well, in the long run, when you coverage your half a million dollar salary, the OMA step program will run out, while the 25% discount is there.
Why would you NOT get both? It just makes no sense. The companies will pay out according to how much you've covered with each company, is my understanding.