[MakeMeFamous]

For swing trading, I prefer to pick currency pairs that has a risk currency on one side and a safe haven currency on the other. This is because it provides the greatest 'disparity' between the two currencies and will usually react to market sentiments on 'risk on' and 'risk off'.

Some e.g. of these currency pairs are: EURUSD, GBPUSD, AUDUSD, USDCAD, NZDUSD, EURJPY, GBPJPY, AUDJPY, CADJPY and NZDJPY.

For scalping, it is not so much about the currency pairs than it is about the time frames. Specifically, scalping is usually done on time frames that are below hourly charts, such as M15, M5 and even M1. This is because it is 'get in get out' trades for 5 to 15 pips.

I am currently using FXPRIMUS. I like that they offer one of the most competitive spreads in the market. For example, spreads for EURUSD is usually less than 0.5 pips and spreads for GBPUSD, EURJPY and GBPJPY is usually between 0.5 to 1.5 pips. :)