I purchased Cornerstone several years ago, primarily because I had heard good things about their support. I have contacted support several times, once or twice with bugs and several times to ask questions. They were always very responsive, and I've been happy with my choice.
Cornerstone also has a good educational discount if you're a student.
I do wish that when viewing the history of a folder you could view the changes to individual files within that folder the way you can in Tortoise on Windows.
