As a player, I picked the hippogriff, because everybody picks griffons. (Which is a little odd, if riding a hippogriff is like riding a horse, wouldn't riding a griffon be like riding a lion? There are not a lot of riding lions mentioned throughout history.) A friend of mine got a hippogriff mini recently in a Heroscape set and we were all commenting on how you see lots of griffon minis, but relatively few hippogriffs. (Also, shouldn't a hippogriff be part griffon, part hippo?)
I'll grant that of the two, griffons are the sportier model, but I myself drive a Honda. That to me is the reliable hippogriff, the Civic of D&D flying mounts.