The 6.x branch of TrinityCore has been created almost 11 months ago and according to the TrinityCore forum download counter, the 3.3.5 is still the most used branch by the TrinityCore community.
In fact, all of the download counters (week, month and year) are showing that the 3.3.5 database has (the more or less) twice of the downloads of the 6.x one.