(Don’t let the title fool you: I’ve only tried out one of these tools so far.)
Marek Kiczkowiak’s post in defense of Memrise as a teaching tool inspired me to create Memrise decks for my own students. Following Kiczkowiak’s suggestions, my decks were designed to supplement coursebook material with grammar as well as vocabulary practice. The results were mixed (in case you were wondering): those of my students who used the decks appreciated them, but I think mixing grammar and vocabulary flashcards made the exercise less challenging than it should have been.
Jennifer Wicks’ post on Quizlet as a vocabulary learning tool is more of an overview of its main features, and is light-on for ideas about how to incorporate it into lessons, but it has motivated me to try it out with my students. I’ll let you know how it goes.