Train's prayer, at the Chaos Altar in the wilderness Chaos Temple.
The Chaos Altar provides grants 3.5x Prayer experience per bone, the same bonus as a gilded altar with two burners lit.
So why use the chaos altar over the gilded altar?
There is a 50% chance when offering a bone on the chaos...
Get two-factor authentication, I also don't see why RuneMate would risk their reputation and exponentially more long-term money, on hacking petty mills, does not make sense.