I'd say whichever has the least vegetation along the river for your "new to you backcast". ;-). I still lose a lot of fly's to the trees, but recall it was much worse when I was younger...I've only been to the Deschutes out of your list, and after seeing the "Seasons on the fly" show on sunday about the Deschutes, I made some tenative plans to go down there. Welcome to the tribe....Tom