Apply one system to many things or become an expert on one thing and only trade that?

What's the best approach to take with trading?

Have one system and apply it to many different things such as stocks, indices, commodities, currencies, etc., in other words, be an expert on the system and use it diligently to take profit from a variety of different markets on which you have little or no expertise?

Or...

Become an expert on one individual thing, such as Gold, and trade that one thing, not according to a system, but instead by having a constant and acute awareness of everything that might affect the price of that thing, in other words, a more 'fundamental' approach?

It depends.

For LongTerm trading, most have one mechanical system and run it against multiple markets for diversification.

For the ShortTerm traders, most will say you need to become and expert on the One Market you want to trade. Know the Volatility, Best trading times, Fundy(ies) and specialize.