3m seems more towards experienced installers. They give you guidelines, throw some vinyl at you and tell you to have at it. They do walk around and help you with tips, steer you in the right direction .If I wasn't wrapping for awhile.befote I took the course, I think I'd be lost though. You should know at least the basics / have some wrap experience.
I've hard Avery is great. Vvivids class is also pretty good for Learning... You'd have to travel to Ontario Canada though. Ckwraps tutorials are great on YouTube, and he's the one who teaches the class.
I've only taken 3m, so just going by what Ive heard. The courses are good for Learning the dos and don'ts of wrapping, but 90% of your learning will be from experience.