Hi there,
For cellular we don’t recommend anything below 1.2.1 (Lots of fixes + device vitals).
We currently have DeviceOS 2.0-rc.1 (Alpha - not really alpha, but the first public release, but definitely not final 
) out in the wild and this will form the basis of our LTS release, a stable deviceOS with no changes, bar bug fixes, for the next 12 months. 2.0/LTS should be considered the most stable version on the Particle platform.
See this post by will for more details on LTS: Tips for deploying reliable LTE Boron that stays up
I recommend that you test on this version and alert us to any issues so that we can implement fixes before Beta and finally GA release.