I've been flipping between Jerboa and liftoff. Unless I'm missing something Jerboa doesn't have the downvote arrow. Not that I ever downvote anyway. But besides that, I think I like the feel of Jerboa better.
Sort options seem better in liftoff though (again, unless I'm missing something in Jerboa).
I'll probably give infinity a try now because of this post.
I think it'll give you some pictures that it knows the answers to, just to actually make sure you're not a robot, but if you get that picture correct, it'll serve you a picture that it doesn't know what the correct answers are, and you teach it by answering what it assumes it's correctly.
Aha! That's good to know. Thanks!