depends on your personal style. no indicator will be the 'holy grail' or something that will just automatically make you income. some people like EMAs or SMAs. Others like to use that with Stochtastics or CCI or other oscillators. It depends what it accomplishes in your system and how you use them that is most important.
I tried to use Moving Average, I think, it is the simplest one for beginners. But I`m not really sure, that it is useful. It helps to identify trend direction, but actially, it is well-seen in most cases without any indicators.
Anyway, most experinced traders say, that using of indicators is not really helpful and reliable. It`s better pratice and soon, you`ll be able to predict chart movemet without any indicators
Surely, you can start with moving average trading indicator, this is one of the most popular default trading indicator! The main advantage of using MA is, it shows dynamic support and resistant levels perfectly! But honestly, all of default trading indicators are useful and you need to analysis on technical tools with proper dedication! Whatever, indicators are useful for clarifying your trading entry point, don’t try to rely on only technical tool either its default or custom indicator!
As you are a beginner, you can start learning MT5 platform as it is the evolution of MT4. The indicators that I am using is the RSI indicator as the signals that gives are clear. Also, MACD and stochastic oscillator are very useful to identify the trend.