A bunch of the old guard were paddling on the middle fork of the salmon this past week and had this very conversation.
Basically, we decided that in our humble experience the Big South Poudre, Linville, and the Tareau (in Quebec) were our favorite committing, class V, longish, single day runs.
All three have very different characters but ae similar in that they are all just so committing, so long, and chock full of oh so sweet boofs.
bp
PS the middle fork of the salmon is OK too

