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.
My DuoLingo stopped showing ads a while ago. No idea why.