More gold-efficient due to higher level, and extra bronze soldier is good if you're using them to level (if you're selling them than better for gold if drop rate disparity isn't too vast). Whether it's better for unit XP depends on drop rates (the reason BS II is better than the 51-charisma map whose name currently escapes me, despite that map being slightly higher level fodder with 3 Bronze Armors + 2 Hashims)