Rather than used or new, it depends on where you buy, and on your budget. A quality second hand or outlet dealer inspects a telescope before shipping and specifies any traces of usage. Though it may be cheaper, purchasing from a private individual involves a balance of risk. Used or new, after quite a while of using an SCT you may wish to collimate it. Disadvantage of used gear is 1. no warranty, 2. it won't sell at a high price should you give up your hobby or upgrade to a larger telescope.
Best luck!
Robert