I personally prefer ZBrush over Mudbox, because the sculpting feels better ( feels a bit clunky in Mudbox).
I don't really like the Zbrush interface but I am used to it now so I don't mind so much anymore and in contradiction to Autodesk, Adobe and all the big players, I feel that Zbrush still has spirit, ingenuity and really come up with cool stuff while Mudbox goes for a more solid workflow.

Mudbox layersystem is way better than that of ZBrush ( especially when you look at the finicky sliderthingies in Z), in Mudbox you can paint over a normal mapped character, there's vector displacement and a 64 bit installer( I am not sure if it is a true 64 bit application).
If you look at these packages based on what hey can do Mudbox is the clear winner, I believe that the only reason why Mudbox hasn't crushed Zbrush to the ground is that a majority of the people don't like Autodesk and if there is an alternative to an Autodesk product people will take it.
In my opinion Pixologic really need to do a couple of things:
-focus on their core strength which is sculpting
-Revise their layer system and the buttons( get rid of those jerky sliders...)
-64 bit version, because I think that when even I as not yet a professional am hitting it's limits ( it's getting sluggish around the 40 miljon mark and I have a pretty good computer still), someone who is building the next model for transformers or whatever movie must get annoyed and have to devise workarounds and what not.
- a proper projectfile structure, Zprojects are to heavy and causes crashes with Spotlight and map extractions and I believe that if you just open a container/reference to a file and not every bit of info of the file it would work a bit quicker

I am not worried about retopo in Zbrush I have looked at it and it's this strange moronic workflow all over again, I think I will have a look at Topogun.
For texturing I am leaning towards MARI ( bloody expensive) or maybe bodypaint

I had been playing around with the Fibermesh addition in Zbrush which is kinda fun although not very usefull in production I think, maybe with that fibermesh to curves thing it will be quicker to set up hair in a movie production, but in a game environment I don't see it happening soon.