I have a Maximus VI Hero and the onboard audio on it is pretty great, but definitely doesn't have the switchable OP-AMP that the Sniper does. If that's something you think you would mess with, go for it. If it's something you don't think you'll spend any time tinkering with though, I don't think your ears will notice much difference between the two at stock settings. They're both great boards and I don't think you could go wrong with either purchase, but I would lean towards the ASUS if you plan to overclock later down the road.
The Gene is significantly smaller than the Hero, however, so keep that in mind. The Hero is a full size ATX, the Gene and Sniper are Micro-ATXs. The Gene has the same onboard SupremeFX audio that ships with the Hero, though. It comes pretty close to packing the quality of a dedicated sound card onto an onboard chip, so it's certainly worth considering.