Best MA Trading System?

A very basic trading system is based on MA Crossover. It is mainly related to two EMA indicators.

I wish all members share their experience that which EMA couples are better for this purpose.

I use the 20 & 50 EMA's on 4 hr chrt and also on daily chart. Use 2 strategies: One is the m/a c/o (pretty straight forward) and the other one is I wait for price to come back and touch the 20 period ema and pierce it by an avg that I have calculated and then buy or sell depending where the 20 ema is in relation to the 50.