I’ve had no luck with any app in particular over extended periods of time. Spotify has been good, but will occasionally only recommend me stuff I’ve heard a million times for a few weeks straight. My best luck has been following music reviewing sites, or going through playlists featuring artists I like on spotify. This is best with smaller bands, there are less generic playlists with them. Finally, my best bet for finding new music from small artists is simply browsing bandcamp. I’ve found many great artists who aren’t on spotify, and many who are.
As a metalhead, I’m a fan of angry metal guy, as far as reviewers go. RABM on reddit is good too.