#13 at CommonGround (or Riverdale Dunes).
I suppose they're ranked somewhere but they're not private or overseas so they don't confer any bragging rights.
Why #13 at Riverdale? I love that course, but that hole doesn't stand out as one of my favs. If anything, it's one of my least favs because the green is so shaded (wet in spring, covered in leaves in the fall).
But, since we're discussing Riverdale now... My personal favs would be #6 and #14. 
Ross,
Sorry I missed your question. I like the Cape-like option off the tee and with the wind against or from the back tee, it's not an easy shot to carry the junk on the left, especially for someone like me who fights a hook. There are also some interesting features around the green, namely a swale in the front and the deep front right bunker. Another reason I like the hole is that it's a challenging par 4 on a course with a lot of short par 4s, including several good ones, like #14, as you mention. I think I prefer #5 to #6.
The nomination of Murphy Creek #3 is a good one.