I'm a Canon/Nikon snob. They're "real" cameras. If you were asking "Which sports would you prefer," it would be like giving the choices of Ferrari, Porsche, Ford Mustang or Chevy Camaro. Like the Mustang and Camaro, the Olympus and Pentax are capable, but they're no Ferrari or Porsche.
A major consideration is the quality and availability of add-ons and glass (lenses). Canon and Nikon both make the best lenses you can buy (short of some of the full frame Hasselblad stuff, I presume), and there will come a time when you'll realize they're worth it.