The fastest cable that connects an iPhone to a personal computer will vary greatly depending on whether the fastest refers to "data communication speed" or "the time it takes to complete charging." There seems to be a change whether the USB port on the PC is USB-A or USB-C (Type-C).
In terms of data transmission speed, the iPhone is always connected to the Lightning terminal, so the theoretical maximum speed is 480Mb / sec, no matter which cable you choose. Since Lightning data communication conforms to the USB 2.0 standard, data communication is performed at USB 2.0 speed even with a USB 3.1 compatible computer unless the USB port on the PC side is USB 1.0 compliant.
"USB-C Lightning cable" is advantageous in terms of the time it takes to complete charging. It is assumed that a USB-C port compatible with USB PD (USB Power Delivery) is prepared on the PC side, but since charging is performed using USB PD, one side charges faster than the USB-A Lightning cable Is completed.
By the way, iPhone 6 and later support input current of 2.1A and 2.4A. If the computer to be connected is a Mac, models equipped with a USB-A terminal support output at a maximum of 2.1 A, models equipped with a USB-C terminal support output at a maximum of 2.4 A, so charging with a USB-C Lightning cable is better Complete in a short time.
Looking at other than PCs, iPhone 8 and later models support 9V / 2A (18W) USB PD charging, so PDO (Power Data Object, power supply that can be supplied as USB PD) is 9V / 2A If you prepare a compatible AC adapter and mobile battery, high-speed charging is possible. Either way, USB-C Lightning cables are definitely the fastest way to charge.