The upper madison is the best bet in my book right now. A slow start to the season has kept the crowds relativeley light and the fish are in really good shape this year. I'm looking forward to getting up there a lot over the next few weeks as the bugs keep getting heavier and heavier. That transitions time between salmonflies and hoppers is one of the funnest times of year up there on dries.
There is so much good water around and not too much pressure.