In reply to Removed UserBoingBoing:
Are you fishing river or lakes, reservoirs, stocked or wild fish, brown or rainbow?
On the whole conditions, feeding time, location and fly presentation (especially the latter) are more important than fly pattern, don't get too hung up on fly patterns unless the fish are feeding specifically on a single food source. Most wild fish are opportunist feeders trying to scratch a life and will eat anything if it looks edible.
The all have preferences at times, the wild browns (small fish) in my reservoir gorge on newts in the spring, also found frogs, mice and big lump of fox s**t in their stomachs - anything goes!