for free online training, the two usually cited are the tony northrup video and the better b roll one. i started with the tony northrup one, followed by the better b roll one. my initial impression was that the tony one was great and the better b roll one was lacking (and downright funny at times - "here's the answer, i have no idea why...".
i then decided to supplement these videos with a paid course, which was outstanding. after completing that one, i realized that the tony northrup video is actually rather shallow. it's useful, dont get me wrong, but he glosses over a LOT of stuff. after the second viewing, i found new appreciation for the better b roll one. the comical moments notwithstanding, he takes the time to go through 100 or so questions and works through the hows and whys of the answers.
so to sum, i don't think anything will beat a paid course. very thorough, each chapter dedicated to a specific topic, unlimited support, lifetime access etc. as for which one, i'll leave that to you. they all seem rather good and it was tough for me to chose personally. very happy with the one i went with though. i would use the better b roll as a great backup, and the tony northrup one as a useful follow up depending on time. also, i would HIGHLY recommend reading through the FAA's own study guide, especially the sections on load balancing and weather. i made the mistake of ignoring it, only to find that i had a good dozen questions lifted directly from that guide (which i discovered when i read the guide AFTER my test). hope this helps