Q: Since you have been tying flies a long time, I figured you'd be a good person to ask - what thread or threads do find yourself tying with most of the time?
A: For the majority of my flies, I use Danville's 210-denier flat waxed nylon. This thread is very strong. When it's secured to a hook, spinning the bobbin in one direction will tighten the thread, decreasing its diameter. Spin the bobbin in the opposite direction, and the thread will flatten. This can be helpful when tying certain flies. You can purchase this thread in all white and use permanent marking pens, tinting it to any color you like.
The other thread I frequently use is UNI-Mono size 7M medium-clear. It's extra-thin monofilament, and it allows all the colors of the material used in a pattern to show through. Both threads come in 100-yard spools and can be purchased at most fly shops.