Glad you opened this thread with that question - i also was wondering which to use - the "latest" stable release or the imscp-maintenance branch from github.
I tried an upgrade from 1.5.3 to maintenance branch on a test system which failed greatly.. only way to get back to a working system was apply the latest database backup and run the 1.5.3 autoinstaller. (btw props fpr the autoinstaller - it self healed everything after this f*up)
I ended up with backporting some of the stuff from the maintenance branch to 1.5.3 for my environment as i needed some newer php and some of the TLS fixes.
And good news that Nuxwin wrote few weeks ago that a new release is in the pipeline! If you are looking for a tester, i'm willed to be one as my imscp "production" instance is just for me, friends and family 