If you need to just maintain the charge of your pad or phone, then anything will do.
If you need maximum charging rates, there are some choices to make. 3.1 A as you found is very good, as long as we talk standard USB 2 or 3 plugs. Many newer devices with a USB-C connector support even faster charging, if the charger has a USB-C connector and supports USB-PD (Power Delivery). The USB-C connection supports voltages up to 20 volts and up to 5 A, so that you could charge with 100 W instead of the old standard of 5 W. You will need a USB-C to USB-C cable though, or USB-C to Lightning for Apple.
There aren't that many car chargers yet that has USB-PD, but a few have shown up.
It is always the device, the phone or pad itself, that decides the charging rate, and takes what is available. So there is no such thing as a "too big USB charger" as long as it follows the rules (5 volt on USB 2/3, 5 volt and up to 20 volts for USB-C)