Go with the Velodyne. I've got an old FSR18 and you can't go wrong. The flat response and near total lack of distortion is seriously addicting. My only complaint is that they cost so much, but they definitely justify it with performance.
The HGS is a great design. A friend of mine did a large part of the design on the HGS and his sample at home sounds great too.
Take the time to hear one. You won't regret it.

SLT