The Amperage determines how long it takes the battery to charge. As long as the charger puts out 5 Volts, it'll work. If it doesn't put out much cvurrent (Amperage), it could take 24 hours for the phone to charge when turned off, but it wouldn't harm the battery. The phone will draw up to the amount of current it was designed to draw, so even if you get a 50 Amp charger, the battery will only draw the maximum it was designed to draw. (A 100 Watt light bulb is designed to draw ~1 Amp. The socket you screw it into can supply at least 15 Amps. The bulb still draws only 1 Amp.)
So 0.7 Amps? Probably enough if you're going to turn the phone off at night and charge it. If you want to leave it on while it's charging, and the 2 Amp charger isn't a lot more expensive, I'd go with the 3 Amp one. (You'd be amazed - or maybe appalled - at the difference in cost of the 2 chargers - maybe enough to buy a whole mouthful of rice. So if they're charging you more than $10 for the 2 Amp charger, head over to Amazon and look for Note 2 chargers [they're 2 Amps and you usually get a USB cable with them].)
