Best Volume Boost apps for Android?

Any idea. There's so much out there, but a lot of it is shit that reduces the sound quality. I still need something to turn up the volume on non-reissued albums at Spotify, because the default volume limit is set after the very loud recent recordings.

So which ones are the best volume boost apps? I need something that works with Spotify. Interested in hints about both the best commercial ones and free ones.

first