are related to each other. They are the 'same' builds, the 'snapshots' folder contain our 'continuous' builds. So one of the next snapshot build will eventually become the next release (and it will be copied into the 'release' folder).
The same apply to the other 2 links.
I would recommend to stick to the 'dragonboard410c' builds, the reference-platform builds are not maintained at this point, it was an effort to get a single build for multiple boards, but right now it's on hold.
For the dragonboard410c builds, the latest 'release' is of course the most recommended option, this is the which had the most testing so far. If you want to play/test what will become the next release, you are welcome to use the latest snapshots builds. there might be some breakage sometimes, but that's the point of doing continuous integration. If you face issues with any of the builds, please report them here or on our bugzilla. Right now we are moving the builds from a 4.4 based kernel to 4.9. The latest snapshots builds are based on 4.9 , and also Debian stretch, not Debian jessie.