If you are looking for it you will find it. There are plenty of opportunities for glades, marked and unmarked, at both mountains. The snowfields at sugarloaf are usually good in march as well. That being said, Sunday River often has comps that utilize the park, rocking chair, or pipe on a typical weekend. Check the events page because Jib academy and dumont cup take place at the end of march. Sugarloaf, also uses their setups every once in a while and is also closed to the public. As long as their is a decent amount of snow both mountains should be fun.