Actually I think it depends on that what kind of trader you are??? Are you long time trader or short term trader?
If you are long term trader then you must use low leverage because you have to stay on market as much time as possible that your earning will be depend on how much time you may stay on market.
On the otherhand if you are short term trader that just using little deposit want to earn more then i will ask you to use higher leverage but i am not agree to trade as short term trader. The long term traders are really real trader on forex market that they can earn more than short term trader though they have take much time with a single trade.