Apple Music vs. iTunes Match I am a prolific Garageband user, therefore I have lots of my own songs in my iTunes collection, which obviously will not be available via Apple's music library...

I am currently paying for iTunes Match and Apple Music. If I were to quit using Match, would I still get my own songs via upload to the cloud or whatever, or would I only be able to access Apple's music? I'd die if I couldn't stream my garageband projects to all my devices.
Apple has a quit informative support-article that addresses the differences between Apple Music and iTunes Match. Both include the iCloud Music Library witch can store your songs, the main difference between both services is what will be stored within this library:

iTunes Match


When joining iTunes Match, it matches all your local music using the sound profile of each song.
If the song is available within the catalogue of iTunes, it is added to your iCloud Music Library and made available to download or stream on all devices as 256 Kbps DRM-free AAC.
Songs that are not available in the catalogue are uploaded to your iCloud Music Library without any changes. Likewise they are available on all your devises.
If you cancel your iTunes Match subscription, all songs already matched can be played or downloaded open end as there is no DRM in place. Only new songs are not added.


Apple Music:


When joining Apple Music, you local music is matched against Apple Music's catalogue using the meta-data of each song.
If a song is available within the catalogue, it is made available on all devices via Apple Music (similar to how you can click on "Add to library" upon every song in Apple Music). Songs can be streamed or downloaded on all devices, but will always be DRM protected 256 Kbps AAC.
If you cancel your Apple music subscription, these songs will no longer be playable, downloadable etc.
However the songs in your local library you initially matched against remain unchanged (no encoding, no DRM) and can be used as before.
Songs that are not available in the catalogue of Apple Music are uploaded to your iCloud Music Library and available on all your devises. I could not find any information regarding DRM or encoding changes for these "unmatched" songs.


Apple Music and iTunesMatch:


When both are used, songs are matched and made available as described for iTunes Match (no added DRM etc.) and Apple Music just acts as a streaming service without interfering with your local files.


So to answer your question directly, your own projects would continue to be available on all devices if you would just use Apple Music.