There is no best carrier, there is only best packing. Joking apart, for brass instruments and the like wrap them securely in plastic, put them in an appropriate box with spacers underneath them put the lid on, drill a couple of holes either end, and pump in expanding foam till it comes out the other hole. You'll have to break them out, but they'll be intact on arrival. Anything else requires a decent shipping case made to measure. Unless it's transatlantic then I'd send them by truck, less handling more door to door.
Giok