Seriously, it depends on what you're trying to do. You're not going to learn a language using memorization only, and you're not going to learn a language through an app only.
I use quizlet for learning vocabulary, because that needs to be done by sheer memorization. For everything else, I take a course. On Italki you can find people who teach online.
I switched from Duolingo to Babbel a year ago and am a lot happer with that. Unlike Duo, there's no free tier though