Unarmed, the hands are considered equally capable. This is a simplification, and for those who like detail,
GURPS Martial Arts, p. 124, offers an optional rule that increases realism:
When using the "off" hand, you have the usual -4 to skill (and therefore -2 to Parry) and -2 to ST (giving -1 to punching damage).
Please note that skill
and ST are affected. That rule goes on to say:
In campaigns that use this rule, Off-Hand Weapon Training becomes a Style Perk for all barehanded striking arts, and it and Ambidexterity (p. B39) eliminate both penalties.
This covers those schools and teachers that feel it's important to train both sides equally, which is a common but not universal exercise. Talk to any boxer about the extra work required . . . that's the work of learning this perk.