Personally I would like to upgrade to v9 (USB3.0 !!)just to play with some of the features, but so far I am just fine with v7. Although, I found that v7 had some issues with running Win8 as the host machine. But after finding a fix, I've had no further issues with v7.
The one thing I keep hoping they will add is the ability to boot a VM from a USB thumb drive. I use some DOS and Linux tools that I use on physical machines when they boot up, but I can't do the same with a VM.
OG