May I slip in a question?
Which is quicker; to charge a phone via the mains socket or a computer USB port?
Without intending to contradict B'cat who, I see, has posted while I typed...
Usually there will be no difference, although it is likely that a respectable manufacturer's own mains charger will be optimal as designed to match the device, and therefor charge the fastest.
As I understand (happy to be corrected) manufacturers may choose to provide devices that charge faster when connected to suitable chargers that exceed basic USB requirements, and provide a more generous current.
I believe (again, may be wrong!) some iPads/ iPhones behave as such and, when connected to an Apple charger, will charge in impressively double-quick time. When connected to more 'basic' outlets, whether PC or wall-mounted that may limit the charging current, it may take longer.