From the Flutter wiki:
Flutter has the following channels, in increasing order of stability:
master
The current tip-of-tree, absolute latest cutting edge build. Usually
functional, though sometimes we accidentally break things.dev (The dev channel was retired as of Flutter 2.8)
The latest fully-tested build. Usually functional, but see Bad Builds
for a list of known “bad” dev builds. We continually try to roll
master to dev. Doing so involves running many more tests than those
that we run during master development, which is why this is not
actually the same to master.beta
Every month, we pick the “best” dev build of the previous month or so,
and promote it to beta. These builds have been tested with our
codelabs.stable
When we believe we have a particularly good build, we promote it to
the stable channel. We intend to do this more or less every quarter,
but this may vary. We recommend that you use this channel for all
production app releases. We may ship hotfixes to the stable channel
for high-priority bugs, although our intent is to do this rarely.
So, use whichever channel you feel comfortable with, meets your needs and/or has whichever fixes in it you need. Start with stable and go from there.