I use the latest version I can.   I have Poser 5-12 on my computer and except for Poser 8 which won't run due to Windows updates that killed several of the IE features (due to security)  I have used most of them in the past year.  Mostly to see what has changed and at which version.  I can run 8 on an older PC that still has windows 7 when I really want to.  The problem is when I run that computer I realize just how slow it and the programs were.  I like SuperFly because it is easier to use and make materials for.  I am waiting for Poser 13 with the newest Cycles engine to really speed up SuperFly.  

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13