I personally really like the MCAT QOD prep questions but some are definitely better than others. This is one of my recent posts on different thread "What helped me was just starting every day with one MCAT question and set a goal for myself to never miss a day. Since starting is always the hardest part, doing this question every day set the tone and got me started for the rest of the day. There are a few of MCAT QOD sites but I really liked Motivate MD's questions since they sent me an email every day and have legit explanations for the answers, so I actually learned something. You can sign up here:
http://motivatemd.us14.list-manage.com/subscribe?u=3e23029b05b4aa341aa8fb4f6&id=cf7defe62e. Besides that the only other material I bought were practice tests from AAMC, which also helped a ton! Hope this helps!" They also have a MCAT subscription that gives you tips and more questions -
http://www.motivatemd.com/mcat-subscription-for-success.html