Me personally would use Fibonacci retracement, how bout you?
If youre a good trader, by just looking at the plain chart you can know already where the market is heading and only need a few indicators to confirm that analysis. I personally used RSI a lot and this will be my choice if I only have 1 indicator to use. Since Im a long term trader I think this can work perfectly for me, were still lucky to have other indicators available for us any time, that can be a big help for our analysis.