Which do you think is better?

Post why you think it, your favourite type or anything else related.

I like devils more because their structure makes more sense. Their lawful nature makes them just that more reasonable to summon as an adventurer as they will do almost anything for your soul. Also all of the Archdevils are really cool.

Tough question. I think devils make for some interesting stories, their law-aspect giving them some range, but I prefer demons as villains.

I prefer Devils, over demons, as NPCs and demons over devils as bad guy fodder.