In fourth edition their alignments become evil and they were classified as devils. Designers thought their scheming fit more with devils than demons.
The succubus of 5th edition is a neutral evil fiend. Honestly given the nature of succubi, I think I like this the best. This makes them free agents that work with all types of fiends. Also, 5E doesn't differentiate between incubi and succubi. One can simply choose it's gender. Previous editions gave incubi separate stats.
What do you think of the changes? What's your favorite version?