Thank you for asking! So the only time I’ve attended classes was for one semester at Sogang KLEC. At that time I had already self-studied for around 3 years, and I found that the grammar I had learned was way ahead of what we were taught in class, but my listening skills and confidence speaking were way behind. The people in my class who had studied at Sogang since level one had learned in a much shorter time than I had. After one year studying Korean I learnt a lot and could read and write well but I could not speak or listen at ALL. So classes definitely have advantages in that they give you opportunities to practice, review, do activities, check your level, get feedback from teachers etc. which are all great!
That being said, I prefer self-study way more and like to study whatever I like as well :). I was bored in class and wasn’t motivated to do homework or review vocab or whatever. My advice to stay motivated and organised when self-studying is formal language exchange! This doesn’t mean just free-talking or online chatting with people but setting up regular times to meet every week with other people who are serious about studying. You can check and give feedback on each other’s writing, do speaking and listening activities together, review what you’ve learnt that week by specifically practising those things, or whatever works for you both.
I’m also interested in this because I always wondered whether I should go to classes before. If anyone else wants to share their experiences of self-study/classes please do!