I chose the Griffin, overall I find the it the most useful. Based on how often I use each mount my order is Griffin, Jackal, Springer, Skimmer, Rapter, Rollerbeetle, Skyscale. The Skyscale will probably move up on the list as I get used to it, but unless they make significant changes I don't see it supplanting the Griffin. I have the Warclaw but I don't do WvW so it's basically useless for me, though I might use it while I'm waiting on an event just for a change.