Eventhough there are some popular MA values like 20-50-100-200, it’s best to find the most convenient MA value for your time frame and your pairs. Start from 5 MA on your popular pair and time frame and increase one by one. You will see an MA which is working as major support or resistance. This will be the best MA value for your pair and time frame.
Well it is a matter of choice and it is hard to tell you something unambiguous. I use EMA 100 on 1H chart as auxiliary tool for determining trend power, while my fellow uses default MACD on the same timeframe and it goes quite successfully for him. Personally, I adhere to the opinion that any indicator and its type work with the market, but only at particular times (not always even when you get divergence cross). That’s why it requires trader to understand the market clean.