Could you tell me what is the worst type of scoliosis?

Probably a left : thoracic scoliosis due to an underlying neurologic condition like a tumor. However, there are many types if scoliosis that may be severe or lead to progressive curves such as certain types of congenital scoliosis as well as some idiopathic scoliosis that progress in spite of bracing. Even curvatures that occur with older age & in people with poor bone density leading to severe deformity & pain.

Large: In general, the larger the size of the curvature the "worse" the curve is.