Which Way?
 

I have also posted this in the North America section. You will see why.
Should I buy a bike in the southern states (USA) and then ride south through Central America down to Argentina/Patagonia, or am I better off buying a bike in Santiago or Buenos Aires then riding north?
I'd really appreciate your thoughts. Thanks a lot.

Buy a U.S. bike in Buenos Aires and than ride back. That way you do not have to worry about shipping and you will be riding 'home' instead of away from home.