Our 2.9 release is a Community release, meaning that it is not an officially supported enterprise distribution. We generally recommend
people go-live on Enterprise, as Enterprise is a certified version of Community that we provide patches and maintenance releases on for
subscribing customers when they fix filed support cases.
Now, with respect to the relative stability between either 2.1 or 2.9 Community, there's probably no real difference. You should probably
make the choice based on whether or not there are capabilities you need in 2.9.
We will be releasing an updated 2.9 Community in June, which adds all the 2.2 WCM Enterprise fixes and improvements. You can read
about the 2.2 enhancements on our wiki.
The current 2.9 Community is effectively "GA" - meaning, it's posted and available for anyone to use however they like. Enterprise (what
you mean be getting at with GA, i.e. certified and tested code) versions of our Community release are available only to customers on
subscription. There's no functional difference generally; mostly just bug fixes that roll back into future Community releases at a later
point in time.
Kevin