How the camera handles from its weight (with lens) plus its button placements.
What annoys me about the D7000 is the placement of the WB and ISO buttons which isn't fixed in the D7100 other than that everything falls easily to hand. I've also got an OM-D which with the additional grip handles quite well apart from the odd placement of the power button.
The Nikon has the superior focusing for moving objects, the Olympus is quicker focusing for static items. The Nikon is easier to get DoF the Olympus is harder not to get everything in focus you can shoot wide open most of the time.
The Olympus has in built image stabilisation (like Pentax) which means with a suitable adapter you can use just about any lense. It's also a lot lighter than the Nikon but the battery charge lasts a fraction of the time of the Nikon.
Picture there's nothing really in it, I just use what is suitable at the time or what is to hand or charged.
Go for what you feel comfy with and enjoy oh and don't forget Tokina for a lens choice too, I'm mulling over the 11-16mm and as my D7000 has the internal auto focus motor to drive the older lenses that lack an internal autofocus motor I should be able to save a few quid.