What is Your Favorite Fly Knot?

I never knew how important tying the correct knot was when it comes to fly fishing until I had some break offs. The knot is the key between you and the trout. Ninety percent of the time you are fishing with tippets and leaders so light that the slightest surge will either break the line or break off at the eye of the fly. Probably the most common knot is the clinch knot. I know that every fisherman or fisherwoman has their favorite. I prefer the loop to loop and the clinch knots. These were some of the first knots I learned how to tie and I have never swayed away from either. Killroys has some excellent illustrations on the following fly fishing knots,

Clinch Knot Duncan Loop / uni-Knot
Surgeon's Knot Barrel Knot / Blood Knot
Surgeon's Loop Perfection Loop
Albright Knot Nail Knot
Backing to Fly Reel Loop-to-Loop Connection
I am curious to know what fly knots some of you are using and why. Give me a comment.
P. S. You can watch the knot illustrations through video if you perfer. All the knots listed above are covered in the video. You will need to wait a few seconds between each knot presentations to see the next knot tie.