When I was just starting out fly fishing, I was content to just put any indicator on my fly line. The task of nymphing was too daunting to be concerned with something as seemingly as arbitrary as indicator choice.
But now, after seeing countless fish physically move away from my casts as gaudy indicators were plopped over their heads, I began to examine the available options in the indicator market.
Long story short, there is no such thing as a perfect indicator. But you can carry a couple of different types to help you out in any river situation. Here is my indicator setup and how I use each type.