Both are located in Middle Hirafu. Would suggest the walk between them is less than 5minutes assuming ok conditions.
The M Hotel is marginally closer to the bottom of the Ace pair lift. nisekotourism.com/en/…Vmap_en1206.pdf
That said, the Ace Pair lift can get crowded as all the guests from the Vale/AlpenRidge/NBS ski school etc queue for an old 2person lift. You may find it nicer to catch a free shuttle bus up to the Hirafu Gondola (or drive up if you have a car).
The M hotel is on Momiji Road which has restaurants like The Barn, Ezo Seafoods(awesome fresh crab; family friendly) and Yosaku(great kushiyaki;family friendly) as well as being next to the Splash Bar. Personally I prefer somewhere a bit quieter so would choose Setstgetsu.