more hits
less hits
For the record, XP comes from HP loss, not number of hits. Armor is beneficial for training because the increased number of hits means better damage distribution across limbs, thus more hp loss before being downed and needing to rest. ie,
Nude: -67 Larm, -105 Stomach. Downed in 2 hits for 172 HP of xp.
Crab Master: -60 Head, -100 chest, -90 stomach, -80 Larm, -55 Rarm, -64 Lleg, -44 Rleg. Downed in 30 hits for fuckton HP of xp.
Technically the big chunks removed by being nude is "faster" as in more xp per hit taken, but the issue with training is recovery time, and the latter way gives you so much more xp loss before next rest. Of course, both means pale in quantity versus playing Up-Downs, which is also enabled by wearing good armor.
Ditto for dealing damage. A sword dealing 20 HP per hit is more likely to deal more overall damage spread across all the limbs as opposed to a sword dealing 120 and dropping an enemy on first hit. However, dealing xp is multiplied by the difference in combat stats, so high level targets are better for training for two reasons.