I find a combination of both for me. When I first started and knew practically nothing about sewing or quilting at all, and I took a beginning rag quilt class. It was baptism by fire but I learned a ton and with that background I was able to look things up on Youtube, etc. and work on my own. If there's a really new/different technique that I need to learn I prefer in-person instruction. I can confirm I'm doing things right, etc. I can hardly ever do anything by just reading - if I'm following a tutorial I need pictures and/or video. Once I get more experience, that may change, but I'm a very hands-on learner.
The classes also force me to get started and work on a project - sometimes I'm so concerned about doing it wrong I never even end up starting!