In my opinion, EUR/USD is the best to trade in. It offers high level of volatility which is good for trading and making good amount of profits.
what i personally trade in is EUR/USD, GBP/USD & AUD/USD.
the funda is simple, make sure you're well updated with the major fundamental news and track the markets regularly initially to understand the trends . Once you capture the scenario all you need is to keep an eye on the fundamental news. it helps to a great extent.
if you noticed here, i prefer trading the pairs with USD in the picture. US Dollar has the biggest economy and any changes to it brings about good amount of volatility.
also it is inversely proportional to Gold prices
so u can trade in the commodities as well and earn some neat profits there too