The stock charger is 2.1 amp IIRC, (either 2.0 or 2.1) so you'd probably be find with the 2.1 amp one. Yes, higher amperage usually charges faster, and should not reduce battery life.
Your 1.3 amp port will, assuming everything is going to the phone, charge a completely dead battery in two hours. (i.e. if the phone is on, whatever you're doing with it takes away from the charging amperage.)
I think the only issue with higher amperage is that it can get a bit warm. Not enough to damage the battery/phone, but higher amperage means more heat from electrical resistance.