The problem with every app like this is the lack of good quality material. For language learning, I prefer learning whole sentences as examples of an appropriate context. But creating good lists of sentences & translations is cumbersome and just throwing a tool at the "crowd" doesn't automatically get you quality content.
That said from all these tools I prefer anki since it has a web-based UI and an android app.
You definitely are correct and I agree with you 100%. The problem is that you can't just throw a tool at people and expect it to stick - ultimately people need good content to study. For us at https://www.memorangapp.com it comes down to two things: (1) Better collaboration and (2) Pre-made expert content. The latter takes a lot of money and time as we've effectively split the tool into a publishing platform and technology platform in parallel. (You can see an example of the expert marketplace of content at https://www.memorangapp.com/premium).
You can check it out at the website and there's another discussion in this thread. We have a web-based UI and Android/iOS apps currently. Brand new versions of these are being released next month as part of a 2.0 launch.
I would happily buy pre-made decks, but for decks I spend hours crafting myself, I want to know I have access them forever and not lose them if you get bought out or go bust.
Currently you can export the HTML and also as printed sheets. In the next few months we'll enable exporting to formats such as csv/tsv. (This is currently supported in the admin interface, but we haven't made it a user-facing tool yet).
If it's any consolation, we already prepaid the next 2 years for AWS and are cash-flow positive. (i.e. not going bust anytime soon).
There is a lot of decent free material on quizlet, you just have to dig. I prefer to import it into Flashcards deluxe http://orangeorapple.com/Flashcards/ because it's easy and even after years of using Anki, I still can't stand it's interface.
That said from all these tools I prefer anki since it has a web-based UI and an android app.