Some respectful nominations for your consideration:

1. Most exciting floats I'd take with somebody elses boat.
a. Upper Nisqually
b. Calawah
c. A whole lotta rivers in the summer or during low flows.

2. Most scenic, challenging, fishy and long floats I will do in MY boat. (Companion boats recommended.)
a. Winter (higher flows only) - Upper Humptulips. What can I say but thank you, RSM. Bill, I noticed you only mentioned the one that is now closed to fishing, hope I didn't give this one away.
b. Summer (high flow recommended) - Klickitat River. Make it a 2-3 day float through the canyon and have some fun in the sun. Be on guard for snakes and the rocks. A buddy landed a +/- 40 lb salmon from the dark chocolate flows.

3. Most incredible drift boat trip I will NEVER do again.
a. Upper Cedar River in the watershed. Incredible, because it is simply the most gorgeous, pristine and untouched stretch of ROYAL blue ribbon trout water I have ever seen on this planet (yes, that includes AK, MT, UT, & CO). I will never do it again because it will never be allowed again and even if it were I wouldn't use my boat. This one time event was santioned by all the proper authorities who were looking for a fool to risk his life and craft to plant fingerlings throughout the upper stretch for a wild steelhead enhancement program sponsored by the So Lk Wash TU back in the 80's. If I remember correctly it took about 10 guys to drag the boat to the river and then help rope it down in many places. Without their help the city authorities would have had us take the sterilized boat out in pieces. We even had to pack out our piss. Got some great photos though. I'll try to find them.

4. Most scenic, wild, fishy and underrated float for both novice and expert.
a. Upper Skagit

5. Insane floats I've had enough sense not to take.
a. Green River canyon. Palmer to Flaming Geyser. OK, maybe the fact that there isn't any real access helped me stay away till I knew better. Boy, am I glad now.

6. Floats I didn't like.
a. None. Easy or hard, I love them all in their own special way. Here are some words to remember:
"Difficulty doesn't make them better and easy doesn't make them safer."
and
"Keep yer hands on the sticks and yer bait in the water."