I thought about paying for DuoLingo because I can't stand the ads all the time and lack of freedom.
But lately I have been doing a lot on Anki. There's some really great decks in there. I also paired it with Mango which has been great as well. Another one that is great is Beelingual when you want to start doing more reading.
TL;DR
Anki
Mango
Beelingual
