Most popular Oracle Mystery?

[Zwordsman]

I l8ve stone. But I love throwing rocks, and later being allowed in my game to throw special metal materials as special rocks. I had planned a called elemental adamantine stone. Never got to though.
I love the explodong rock too, and the swift action aoe is fun
I do wish it got a stone ramged spell, along the lines of a bigger acid splash, or a bludgeon version of i0snow ball

[Treefolk]

My very first PFS character was a stone slinging oracle/paladin of Erastil (mystery of stone). To date however, my favorite mystery that paizo has released is the Solar Mystery (from the Harrow Handbook). It balances flavor with mechanics to get a really unique mystery together (I'm disappointed by most of the mysteries as there is a lot of needless over-lap between them all).