If you're looking for a simple easy to manage model of cartilage differentiation, ATDC5 cells are a good cell line, easy to transfect, maintain and differentiate.
C28/I2 is a Human Chondrocyte normal Cell Line that is immortalized via retroviral vector-mediated simian virus SV40 Large T antigen expression. but retroviral cassette was selected for using G418, such that the cells are already resistant.