I'd have to say that my overall favorite stage is Maple Treeway. I just love the way it twists and turns, and I enjoy stages with cannons, since they let you avoid those dreaded Spiny Blue Shells.
My favorite part of the course is the u-turn section with the trick ramp. I enjoy speeding up twice on the boost panels, then grabbing an item mid-trick. That one area often helps me get ahead a couple of positions, and I just like the feel of the curve. Other than that, some other stages I enjoy are Koopa Cape, Sherbert Land, and DK Summit. Some stages I just positively hate are Moonview Highway, Grumble Volcano, Ghost Valley 2, and Wario's Goldmine. I must just have really bad luck in those places or something.
Coming soon to the Kanto Safari Zone...