I studied for 2 weeks using QBank, just got my scores back, and shockingly got a 259 (don't usually do that well AT ALL on standardized tests), which I am still pretty sure is an error that the usmle will be contacting me about to correct shortly.
In hind sight, I might have went with World had I known about it BEFORE paying for a month of QBank just because World is cheaper. I did do one block of World questions to compare, and I thought the answer explanations for World were better organized --> short and to the point... just how I like it. Kaplan explanations seem to be written by different people, and some of the writers ramble on and on making it hard (at least for me) to pick out the salient points.
But, I thought the question stems in World were too short. The longer questions in QBank, in my opinion, help you a little more with stamina, etc for the real thing. Also, I don't know if they have recently changed QBank or if I am ******ed or what, but I sure didn't think the QBank questions were easy like I have seen mentioned repeatedly on these threads.
Basically, I know most people on here swear by World, and that's probably not a bad idea as it is cheaper for the same # of questions. But, I think you can't go wrong no matter what you choose. After all, it's probably the mind-numbing task of doing the questions that helps in the end not the questions themselves.