For me, the challenge comes from catching a fish with a fly that I personally tied and preferably one of my design. As for techniques, I let the water dictate what is required. It may be on top, it may be tight-lined with lots of weight, it may be with an indicator or a sink tip with added weight to dredge deep runs. Likewise on still-water i may be a weighted streamer, bassbug or #18 bead head nymph under a popper. Whatever I need to get to where the fish are. But I let the water tell me what I need. Fact is, my favorite type of trout fishing is prowling pocket water with attractor dries. But not because of perceived challenge, its because I enjoy it the most. Which is the reason I fly fish to begin with.....the enjoyment. Not the challenge.