[General Topics] TheMystic:
There are still users who rely on locally saved music files instead of using music streaming services.

Advantages of Music Streaming Services:

1. You can find pretty much anything (there could be some exceptions)

2. The music is complete with all details such as Artist, Album, Genre, Lyrics, Composer, Album Art, etc.

3. You can create playlists that will SYNC to the cloud. You'll be able to access them from any device, anytime, anywhere.

4. Your history and activities are platform independent - they will be available on Android, iOS, Windows, macOS, Linux.....everywhere!

5. You don't have to worry about losing files or them becoming corrupt.

6. You don't have to waste time searching, downloading and fusing metadata into your files.

7. You can save your phone's storage for something else.

Disadvantages of Music Streaming Services:

1. There is a subscription to pay.

2. You'll need internet access (unless you download everything).

3. Slightly more battery usage if you're always streaming over internet, but you can avoid/ minimize that by downloading them to your device.

With the above out of the way, let's see how best to manage your files (those that aren't downloaded using a streaming service):

The first step is to add METADATA (or TAGS) to your music files. This means adding all the required info (Artist, Album, Genre, Lyrics, Composer, Album Art, BPM, Track Number, Disk Number, etc.) into the music file itself. This can be a daunting task if you have too many music files or if you want to add too much information. There are software tools that can make this job easier for you, but you'll need a Desktop (preferably Windows) based tagging software that can automatically play your song one by one, identify it, download the required info from the internet, and add them to the music file itself. You can leave the computer ON overnight for a couple of days (or more, depending on how many music files you have), and the job will be done. Alternatively, you can add just the info that matters to you, enough to help you create 'Smart Playlists' on any device, irrespective of the platform (Android, iOS, Windows, macOS, Linux).

This is a one-time work that requires some time and effort, but once done, it makes music management super-easy, super-efficient, and the whole experience super-fun. Music Tagging software allow you to customize the Metadata/ Tags in several different ways, and this enables you to create 'Smart Playlists' in several different combinations, which will all work in every single platform. They are completely platform independent, so you don't need to create any 'database' using any app or be dependent on it. All the required info are present in the music files themselves, and they'll work on all your devices. Creating Playlists based on one or more criteria becomes just a matter of a few seconds, and you create playlists of hundreds of songs of your choice in just as much time. Most importantly, there will be no duplication of files on your device, even if the same music file shows up in several of your playlists.

ANDROID MUSIC PLAYERS

The most important feature for a music app is its ability to organize your music library!

Yes, I didn't say sound quality because if you have a good pair of earphones/ headphones, your music will sound good even with the stock audio engine.

For those who don't know, there are two types of music apps. One that uses stock media database, and another that builds its own database from your music files. Apps may also choose to either use the stock audio engine or come with their own proprietary audio engine (some like the one below provides both options - you can install their DSP plugin if you want it, and its free).

Player Pro (Paid)

{Mod edit: Link to paid app removed. Oswald Boelcke, Senior Moderator}

Player Pro (Free)

You can use the above app to create Smart Playlists on Android. If you're not happy with the UI, sound, or any other aspect of this app, you can use any music player of your choice to play your music. But to access the Smart Playlists created by this app, you'll need to add these to Android's own Playlists which all music apps will have access to. This is made possible by this app:

Music Playlist Manager by flyingdutchman

{Mod edit: Link to paid app removed. Oswald Boelcke, Senior Moderator}

This app above also allows you to share a playlist of songs quickly to someone who may want it. You don't need to pick files one by one (if you follow any form of folder structure). The app will do this with a single tap that is just unbeatable.

Personally, I have added metadata/ tags to my collection using MusicBee and iTunes (version 12.6.5.3). And use the above two apps on my Android for the purposes mentioned. I can now simply copy my files to any device (dump them all in a single folder) and everything shows up neatly and well organized, in every music app (again, on all platforms). I can recreate any Playlist in a matter of seconds on any device, because they are SMART (possible because of Metadata/ Tags) ! I can also just copy the files I want from a handful of playlists with a single tap.

There are no duplicates, music management is extremely simple, fast and super-efficient!