I beg to differ, choosing a lower wattage or amperage charger will cause slower or possibly no charging (probably just slower). Using a higher wattage or amperage USB charger, if you can find one rated higher than the iPad chargers, will not harm it. The iPad will only draw the current it needs and no more. If it is a poorly designed USB charger which does not meet the voltage requirements set out by the USB standards than it probably will damage the iPad or any other USB device.
The quickest way (and really the only way) to charge your iPad is with the included 10W USB Power Adapter. iPad will also charge, although more slowly, when attached to a computer with a high-power USB port (many recent Mac computers) or with an iPhone Power Adapter (5W). When attached to a computer via a standard USB port (most PCs or older Mac computers) iPad will charge very slowly (but iPad indicates not charging). Make sure your computer is on while charging iPad via USB. If iPad is connected to a computer that’s turned off or is in sleep or standby mode, the iPad battery will continue to drain.
Apple recommends that once a month you let the iPad fully discharge & then recharge to 100%.
At this link http://www.tomshardware.com/reviews/galaxy-tab-android-tablet,3014-11.html , tests show that the iPad 2 battery will charge to 90% in 3 hours 1 minute. It will charge to 100% in 4 hours 2 minutes. The new iPad has a larger capacity battery, so using the 10W charger will obviously take longer.