I understand that if I knew everything in Q-bank by heart I would be fine, but I've already done about through all of it almost twice, and just don't have it in me to do any more, which is why I would like input on the other two.
I found Usmle World to be quite difficult in comparison to kaplan Qbank. The questions went into minute details and often skewed to a step2ish style of asking questions. I would say they are a good buy for the money they charge...and No i am not here trying to sell their product before anyone jumps at me....I just found them to be a good study tool. I have not bought usmlerx hence cant comment on that. I am sure they are good too.
my two cents!