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The charger which your phone came with is 750mA.
For me this charger takes about 25 minutes to charge from 99% to 100%.
The best way to speed up the charging process is to buy a 1.5A charger...
(you can get more than that, but it may harm your battery in the long run)
You can buy any A charger, the higher the better.
Using a higher amperage, like 2.0 or 2.1 will not cause any noticeable harm in the long run. The device takes as much power as it needs and no more.