The best indicator is the type of indicator that is right for your purpose when trading.

The best indicator is the one suitable for the Trader's intended use:

If you want to use indicators to define trends, the best indicators are the moving averages.

If you want to look for signals that the market is moving slowly, there is a possibility of a reversal in the future, you should choose momentum indicators. 

But if you don't understand what the trend is or what the market's momentum is, you should stop looking for the best day trading indicator on google. Learn about technical analysis and the basics before trying to apply indicators when trading.

Do you really know how to use indicators?

Please stay away from indicators that have arrow messages telling you where to buy and sell, especially free items. Such indicators are poisonous for Traders who are new to trading, you will be dependent and it is easy to think that trading is easy (just look in the direction of the arrow, you will not make any profits). But no matter what style you trade, first of all, understand how that indicator works.

Moving Average not working well in the sideways is a simple example

You do not need to learn to program an indicator, but you do need to understand when it will appear on price charts. Sometimes it is necessary to do this by hand drawing the formulas of those indicators yourself. For example, using a moving average is generally quite simple, you need to understand why when the price closes below the moving average, many traders think it is a sell signal. Once you understand the nature of the indicator, you will find it easier to spot noise signals, the times the indicator announces an entry point but is a false signal, you can compare which command better (because no All entry points have a high probability of winning if it only depends on the indicator).

When do indicators work, when do they fail?

An indicator can report the wrong entry point, which is completely normal because every tool has its own error. It will be very short-sighted if Traders believe that indicators are only witty and use price action as the only tool to trade.

An indicator is just a tool and the goodness is up to the user whether your tool is very ordinary. For example, if you understand that moving averages are ineffective when trading sideways markets, don't use moving averages when prices enter that zone; Or don't use the overbought/oversold signals of momentum indicators when you are trading against the trend.

There is no "fool" as trade-in reverse with the uptrend with RSI oversold

The best indicator is not the RSI, MACD, or Bollinger Bands. The best indicator is the one you can use and best suited to your trading purposes. In other words, indicators are best when traders have good skills to use indicators. By the way, you also need to be open to many types of indicators, the more you understand and understand the characteristics of each type of indicator, you may add a lot of interesting trading tools in your own system.