Share your experience!
I got 1.5A charger that came with the phone.
Haven't really measured time but I know that when I charge my phone when it's turned off, it charges very fast.
Please only use approved and authentic Sony Mobile chargers designed for use with your handset. The use of third party chargers with varied voltages may cause harm to your product.
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It takes about 3 hour from 0-5 to 100% to charge with bundled charger (the charger which comes with the phone).
I don't think using a charger rated at 2A will charge any quicker.
In general the phone hardware and /or software determine the current draw (and hence rate of charging), so just plugging in a supply rated at 2A doesn't mean your phone will use that 2A. Since the SP comes with an 850mA charger, it's safe to assume that you phone will only ever draw < 850mA (otherwise it will overload and damage the charger).
It's more important that the supply voltage is a well regulated 5V. Above that, you could potentially damage your phone. Most consumer electronics have some sort of overvoltage protection, but it's really not worth risking.
For Xperia XP I'm using charger for my tablet, it gives 1.5A, and all is O.K. Phone is drawing 1.2 - 1.3A maximally, measured by Battery Monitor Widget app.
Waiting all the time for charging with original charger (850mA) is crazy and bad joke, i think 
as long as the voltage is at 5V you'll be fine with a 1.5 or 2A charger