Good apps to play offline music?

Hello, since the whole Spotify thing got taken down, I find myself wandering, looking for a way to listen to music. My decision is to just download songs and listen to them offline. What app, for android, do you suggest? Possibly one that is free, no ads/anything online, can mark favourites and make play-lists, and perhaps that could make me see the album cover if I downloaded it. Any suggestions?