I've got some questions about leg training, I hope you guys can help:

I've been training now since March and I've always done squats and not leg presses. Until this week there was no problem, however on Monday I had some back pain while doing squats. I have a slight case of scoliosis, and it felt like that kind of pain. My doctor said it wouldn't be a bad idea for me to switch to leg presses, since they don't compress the spine like squats do. Also to avoid standing calf raises and do only sitting calf raises. Of course I want to prevent further back pain, so I don't see any reason not to do what he says. I've always heard that squats are much better than leg presses. Could someone please explain why that is, if it's true, and is there anything I can do to supplement the leg presses? By the way for legs I also do leg curls and leg extensions. Also, if any of you have scoliosis, how has it affected your training? Any tips?