How about a slight modification/expansion to the original question.

1. Favorite pattern to fish.
2. Favorite pattern to tie.
3. Most effective pattern.

With respect to the original question, I tend to mix things up based on factors other than river "size" and/or type. More often, water conditions, what I know about the water being fished (depth, speed, micro-features), and it's likelihood of holding fish.

If I am working a piece of water rather than fishing on the go (gear or feathers) I typically start big and finish small while trying to achieve some sort of color/contrast change in the process. I like the way those intruder style flies look, along with anything incorporating some long and thick rabbit, rhea, peacock, or ostrich to get a lengthy, swimming profile. Action, action, action. If you think color matters, than it probably does. If you don't think it does, than it won't.

Whether fishing with gear or feathers, if I am working a piece of water, I typically start big and finish small, start flashy and bold and finish natural. In the case of feathers, big meaning a 4-5 inch fly or 10-12 mil egg pattern. Small meaning a classic spey pattern or 8 mil egg.

I am sad and glad to say, I haven't put in much time swinging flies for steelhead. In fact, I can count all of the steelhead I have hooked on the swing using three fingers. However, I nymph behind guys swinging flies for steelhead all of the time and usually out fish them 6 to 1 I have yet to witness the swing accounting for more fish than a dead drifted presentation. I am sure it has happened, perhaps with some regularity, but I haven't seen it.

My vote for most effective would have to go to a 10 mil egg pattern in bubble gum pink.