Young gulch, just down the road a couple miles past hewlett, is a notch harder than hewlett and much more shaded if it is a hot day. Hewlett is a lot of fun though (especialy if you do the loop w/ the sketchy descent), and is really nice when the leaves start to fall. I personally don't think Dadd is worth the much longer drive.
The poudre offers some great hiking right now too--you could pretty much hike your tube/duckie down the center of the river all the way down...
Originally Posted by Jensjustduckie
Tubing unless you're into major boat abuse, definitely biking - Hewlett is awesome for biking, some parts are really challenging. Dadd gulch is lower key than Hewlett - it's a steady climb the whole way out so the ride back is really fast and has some good jumps.