The 29 tire will have a greater contact area but whether this is going to make a noticeable difference on the trails is doubtful. When buying many bikes one needs to decide if the size of the tire or the model is more important. My Specialized Stumpjumper was available only with 29 inch tires as was my Scott Scale. If I wanted 27.5 tires I would have had few choices. The bike manufacturers made the choice for me.