It's not the resolution that's the issue in ZBrush, it's Spotlight. It's just way clunkier to get a texture on the screen for projecting onto your model than it is in Mudbox. Mud is super simple, ZBrush is weird what with that wheel interface and all that.
Sculpting = Zbrush Texture painting = Mudbox Sculpting in Mudbox is horrible in my opinion but then using spotlight for texture projection painting is just as painful. Overall, you get more bang for your buck with Zbrush though.
Everyone with experience will tell you zbrush is the standard for sculpting, there are no 'buts or maybes'. That's not to say we don't use both. A lot of people use both. Mudbox is great for texturing but zbrush just overwhelms it in terms of sculpting. Plus pixologic gives you constant updates for free, unlike most apps…