Hi Bretonwoods,
3.2 is the stable release and all the fix we are currently working on or providing are applied to 3.2 branch.
The 3.3 branch is at the moment only used for Zentyal OpenChange related work, fixes and new development with regards to 3.3 release.
Therefore, Zentyal Server 3.2 is the way to go atm.
Best Regards,
Julien.