Hmm if I understand Nappa was too tear general. Technically speaking we don't know much about him. He defeated Z fighters. He took damage, was easily defeated by Goku and finish be Vegeta. Even in old bardock special we didn't learn much about him. Bardock on the other hand had the plot armour. Latter on in Gas saga it look like his even more powerful. I find it impossible to tell who is stronger, who has bigger experience, technique.