Around my parts many different flies work for different fishermen. With a few working for all. Shrimp, leech, green machine, Adams, mosquito, butterfly, to name a few.
I have found fish to be more pickey of color combinations, than actual patterns. For instance, one place I fished produced more fish on lighter, grizzly hackle type flies, with contrast. Light with dark, or dark with light, depending on body to wing and tail. The darkest patterns were typically passed up on. The largest fish I took on a larger dry white miller. I honestly think its colors and combinations that attract the most attention. The lighter earthy tones, green greys, to green browns, to light browns and beige. I really like a little red, and flash added in here and there too. If its the right color and size, and its buggy looking it's probably going to work. Unless of course the fish are very well educated or leader shy.
just me 2 cents worth.