Domestically at least, Fedex Ground is definitely the way to go. USPS is a distant third after UPS, both because they will charge you an exorbitant price and they seem to be the only carrier of the three (and I have shipped and received a TON of bike stuff over the last 15 years or so) that has managed to damage my goods - in both cases, wheelsets, including one where the wheels were packed like they were Faberge eggs.