Answer
The moss tree would have a harder time: it lacks vascular tissue and, so, would have a hard time moving water and nutrients to where they were needed. Also, its gametes would have a very hard time getting together on top of a tall tree.
Work Step by Step
First, consider the basic features of these two groups (dominant generation, anatomy, etc.). The lack of vascular tissue in the moss and the positioning of moss gametes in a gametophyte tree should jump out as major hurdles for a 10 m moss tree to conquer.
