What's the best input for your indicator?

I have been asked so many times about what's the best input for this indicator or that indicator, it is an excellent question, but it's also the hardest one to answer. Based on my knowledge, the best input for an indicator is not a fixed value, it depends on the market(FX, STOCK or FUTURE), profit target and timeframe you test it.

For example, MACD is a very popular indicator with couple inputs, but what is the best combination for it? Assuming we have an input combination which is excellent in 5 min chart for FX pair USD/CAD with a 30 ticks profit target, and we found this combination in a back test range of 2000 bars. But if you test this combination in 500 bars, the result could be awful. Further than that, you may not get the same performance with this input combination on other FX pairs, even with the same timeframe and back test criteria.

My conclusion is that the best input of indicators only exists on certain conditions. The best input of an indicator may vary in different timeframes, profit target and market. One combination cannot archive the best results for all conditions, in order to acquire the best performance, we need to explore unique input combinations in different situations.