Through the barrel jack or into Vin (functionally identical).
Be aware that the linear regulator on the Arduino (or any linear regulator) wastes any input voltage over 5V. In other words, 9.4V (14.4V - 5V) is blown off as heat. To avoid this inefficiency you should use a device with a switching regulator; the guts of a cheap USB car charger would work or you can buy a switching regulator module off eBay (search for LM2596).