Mickelson has to have the most loyal fanbase, going all the way back to Arnie. When you look at the number of times that he was knocking on the door back in the late-90's and early 2000's... took him 13 years to get the first one, at age 33. He's finished 2nd in majors 11 times. So many freaking times it was there for the taking, and a wayward tee shot would begin his demise. His fans have been alongside him on that rollercoaster the entire time.
People will argue that Tiger's fans are the most loyal fans... I don't agree. Tiger was a freak of nature, it's easy for someone to plant their ass in a seat on the bandwagon of a once-in-a-lifetime athlete. But to do that with a guy over and over who has a track record of ditching the plane nose-first into a mountainside only 5 miles away from the airport?
That's loyalty.