Pochomil is the village immediately south of Masachapa, separated by a short walk along the beach. It is the slightly more developed of the two — there are a few guesthouses, a handful of restaurants, and a small weekend tourism infrastructure that Masachapa proper largely lacks. The beach here is the same dark sand and open Pacific surf, and the atmosphere is relaxed in the same way.
Most visitors end up at one or the other without feeling a strong distinction between them. Pochomil has marginally more options if you want to stay the night: look for simple hospedajes near the beach, nothing fancy but clean enough. If you are making a day trip from Managua, the two villages together give you enough to fill a comfortable day without any planning.