Alright so I've had the same question for a long time. The majority points to Chad, but I feel like that is because Mike's is new and nobody has tried them yet. As much as I don't like being the guinea pig, I went for it this time. I am almost done with Mike's O.C. videos and I feel like I have a pretty good insight to share. Although, I have not taken the DAT after watching Mike's videos, take my advice with that in mind.
I watched Chad's GC and OC videos and took the DAT after completing my OC classes. I scored 19GC/20OC.
I have used Chad for GC again and they were the same thing again, I liked them last time, they were helpful last time and same for his OC videos.
I have been following Ari's study guide (not to the part where I have taken exams yet...will update again then and again after the DAT). As he suggested, I used Chad of GC and I am almost done with Mike for OC. I think that I personally like Chad's videos better. Mike's explanations are solid. I feel like he simply teaches all the mechanisms that we need to know. But if you do not watch all of the solutions videos for their entirety, you will miss some important information. Sometimes his quiz questions will have content that he has not taught yet. This is SO FRUSTRATING for me because I realize that there is no way for me to fully know why each answer is right/wrong since I haven't learned the material yet. I would have preferred that he just teach everything in the teaching videos and just answered questions in the solutions videos.
My current conclusion, I think Mike's OC is great to learn the material but the quiz and assessment portions are substandard imo.
I will update again when I have taken some practice tests to give a bearing of how well Mike's videos have served to help me score well on the practice exams and DAT.