Depends also on the size, desired presentation and type of fly, too. For steelhead and salmon wet flies tied on TULE (turned-up-loop-eye) hooks, the double Turle knot seems to work best (for me, anyway) Using a clinch knot will cause flies tied on these hooks to swim off kilter. Also, when using ring eye hooks, a loop knot may give the best results (for lots of salt water flies). Then, there's the good ol' Uni-Knot, which lots of my friends use, but I've never learned to tie. As pointed out above, probably the improved clinch knot will meet most trout fishing needs.
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