I have never gone to a SW class and have managed to do fine from home. However the first time round I tried from home my heart wasn't 100% in it so lasted about 3 weeks, and for the next couple of years I piled more weight on. This time round losing weight was something I really wanted to do so my motivation alone was enough, as well as the support from my lovely OH.
Another reason I don't go to group is the lack of training of some SW consultants receive. Now I know that this doesn't apply to all consultants, but I've read on here many times about people getting the wrong information about the plan straight from their C. Also, my mum and sister go to a group (they've tried doing it alone but they need to discipline too) and I've had to correct them on a lot of things about the plans/syns/free food etc but they tell me it must be right because their C said so!
At the end of the day we are all different, my only advice would be to join a class and see what you think, then you can decide what's best for you.