I'm a big fan of Bob Jacklin of West Yellowstone. Last summer (2014), my son and I were lucky enough to be guided by him on the Madison....between the lakes. We got some really nice Browns.
The fly used? His March Brown Spinner. The fly's namesakes weren't around, but the fly worked like a charm.
This summer, I didn't get to go at the best fishing time. Went in mid-August instead of early to mid-July. The "usual suspects" weren't really working....PMD's and Caddis patterns.
No real hatches at all. I wanted to fish dries, so I finally thought I'd give Bob's fly a try.
It saved my pride. Only pattern that worked. Personally, I think it is the silouhette from below that makes it so enticing.
Poor quality photos taken with my phone, but gives you an idea.