Regarding the Digital Sculpting crown, Its not about who releases first its about who gets the multi-seat orders from the FX houses and game dev companies.
The way things stand zbrush looks like it will be sidelined in favour of mudbox due to mudbox’s streamlined work flow and real consideration of the needs of digital sculpting professionals.
zbrush will always be popular within its community and as a great one of a kind package but commerically something so well ~odd~ as zbrush is very hard to integrate into the pipeline whereas mudbox may well be seen as a drop in tool that requires reletively little training.
Another to aspect consider is confidence in the dev team of the respective companies, we know really nothing of how mudbox will be developed post 1.0, how frequent will updates be, will expected deadlines be met, and will the dev team listen and respond to suggetsions/bug reports/feature requests. Zbrush has already dropped the ball on most of those things and that doesnt instill confidence if you are considering tying it into your pipeline for X project cycles.