Well for me, it is RSI and MACD, both of them are good for the trading indicator and it is free.
But if you will compare these two indicators, statistical studies have been researched that the more accurate is RSI than the MACD ^[1].
On my own. --I did not rely on this indicator while I am in trading, I usually referring to fundamental stuff than technical, because sometimes this fundamental analysis will give a huge impact on the market which is perhaps will be shaken the whole market price.

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^{[1] - https://tradeveda.com/macd-vs-rsi-which-indicator-gives-better-trading-results/}