The quick difference
USB-C is now the common connector on many newer phones, tablets, laptops and charging blocks. Lightning is used on many iPhone and iPad models from earlier Apple generations. The right cable depends on the port on your device and the port on your charger.
Check both ends before buying
A cable can be USB-A to USB-C, USB-C to USB-C, USB-A to Lightning or USB-C to Lightning. Look at the wall charger first, then your device. Matching only one side is the most common mistake.
Charging speed is not only the cable
Fast charging also depends on the charger, the device and the cable rating. A good cable helps, but a low-power wall block or an older device can still charge slowly.
Simple recommendation
For newer USB-C devices, choose USB-C to USB-C. For older iPhones with Lightning, choose the cable that matches your charger: USB-A to Lightning or USB-C to Lightning.