I've done most of them at one time or another. I think I have 4-5triple crown plaques sitting around. I stopped counting a long time ago. The Central Coast Dbl is my home one so I either ride it or staff it. I think I've ridden it 7-8 times over the years. I kind of stopped doing the southern ones back when Hugh Murphy was running them. He was a little spartan on the support. Since Planet Ultra took over I still haven't done any...for no particular reason. If I do one it's usually the Terrible Two, Devil Mtn, CCD, Grand Tour or Knoxville. They charge an awful lot to do those rides and I have a hard time justifying it when I can do a dbl from my house for free.
Plus, I've moved on to ultra's like the Furnace Creek 508, Hoo Doo and RAAM. I'll be on the tandem at the FC508 this year. This will be my third 508 on the tandem.
There are lots of good doubles to break in your stoker on.
I would suggest the Solvang Dble. It's one of the easiest and most beautiful! It's also very tandem friendly. A friend of mine did it in 8:45 on his tandem!