Quick search gave this review: The main differences between Babbel vs Duolingo are: Babbel is best for learnings looking to completely master a language, whereas Duolingo is better for sporadic learners who want to dabble. Babbel offers lessons with conversational practice and cultural immersion, whereas Duolingo offers adaptive learning lessons.
Yeah I used Babbel to pick up some basic Italian a few years ago and thought that while a bit more “boring” than Duolingo, I felt like I was learning more useful stuff. It’s structured more like a language class at school.
Memrise is worth a look as a Duolingo alternative. It’s similar but feels a bit more “serious”, there are some nice features like you get videos of native speakers saying phrases with a variety of accents.
Memrise also has fun sketches that offer something most language tools miss: entertainment. They’re dumb but can cause a little chuckle (extra satisfying when it’s in an unknown language)
Babbel is great and they also have shorter subscription plans. I only needed a quick fresh up of my French skills and did not see why I should subscribe to a full twelve months plan, which was the shortest that I could find on Duolingo.