For outdoor quads, the question one must ask is where you want grass and other debris. If the front/rear of the quad (often where cameras and video antenna hardware is present) is something you want to avoid, run props out. If you're more concerned about keeping the sides of the electronics stack cleaner and don't have the lens of a camera in the prop plane to absorb junk, props in works quite well.
In hybrid configurations, there are some very minor advantages of the rear props having cleaner air available in props-out configurations, and there are a few mixer edge cases with one corner at maximum commanded thrust where the yaw input matches better, but similar ones in turns where it's not as ideal.
All that aside, really it comes down to where you can tolerate high-speed plant material, sandy grit, and broken polycarbonate peppering the middle of your quadcopter.