I'd go with EMS from the post office. FedEx, UPS, and DHL tend to have more issues with customs in my experience, whereas I've only had one box out of hundreds caught in the works when using EMS. China Post is actually quite competent, and EMS offers decent tracking. While I'd still trust FedEx more for sensitive documents or supply chain solutions, for the average individual, EMS is probably the easiest and certainly most cost effective choice.

Whatever you do, don't send something standard mail (non-EMS) using the post office; you'll be lucky if it shows up three months later.