If it were up to me, I would choose to go with the airlines, since it sounds cheaper that way anyway. The USPS service, especially if you are going for their cheapest is VERY unreliable. If they say it'll take 6-8 weeks, expect it in double that. If you do go that route, pay the extra for the insurance and tracking.
Another option would be to wait until you know someone will visit (preferably after the summer 'high' season for airline prices) and have them bring it. It would be almost as cheap as shipping, and you have a set time for someone to visit you, an added bonus.
Personally, I'm still bringing things over slowly, two suitcases at a time every time we go back and forth (or three if we pack lightly going!). Of course, eventually we'll probably be moving back to the States, which will probably involve shipping, selling and swearing.
Best of luck with your move!
Tricia