I've had a pair for a few years now. I ride HOs. A couple dudes on my water ski team ride stereos.
Stereo wake skis are great if you're a bigger dude. they are a little larger than the HOs. Plus, they aren't a continuous tip to tail rocker - they are flat underfoot which makes them a little more stable feeling. CONS - they're bigger, so it's more ski to throw around. Since they are flat underfoot they are a little harder to initiate spins/surface turns on.
HOs - a little smaller than stereos, so a little more ideal if you don't weigh 200 lbs. continuous tip to tail rocker which makes them super nimble. CONS - if you aren't a strong water skier they're super squirrly.