I think it depends. If they have a budget and time they would prefer one on one course but if not they prefer online courses. For me, I prefer online courses I always watch Engvid it's a free tutorial English language. I can check out their vids in my free time so it's very flexible and no payment as well. They have tons of subscribers around the world. They have YouTube channel and a website. It's also good to have one on one course because you can practice what you've learned but it's also nice learning new tutorials in online it's a never ended learnings. You can check out Engvid.com to see what I mean.