Sorry for lack of detail in OP, I was in the dark so wanted to minimize typing! So if terrain is most important factor - what sort of terrain favours each particular type of bike, would you say?
Or - to rephrase it - if you wanted to ride home as quickly as possible from a few miles away and your route home was all off road - through a mixture of gravel paths, with some mud and sand and lots of small rocks and roots sticking out etc, which bike would you pick because you thought it would be faster?