Mike,
The best will probably not be the cheapest ;-)
When I bought my bass (from a US private individual) I was rather worried about the dangers of rough air freight companies and the likes, so I gladly accepted the seller's offer to have a specialised packaging company float the bass in its HSC in a wood-reinforced carton box filled with foam chips for 150 bucks. Together with the 2-day expedited UPS air service it costs me some US$ 450,= to get it here (The Netherlands), but the biggest blow came on my doorstep when the UPS guy also delivered the tax man's claim: 4% import duties over the purchace price and on top thereof 19% VAT over the total shipment value (incl. shipping & insurance).
In Germany VAT is lower (16%) but don't overlook that component because you'll have to pay it when you officially import the instrument into the country.
As for paper works: the seller had made a neat one pager describing the shipment's content & value, saying it was a second hand instrument being sold by a private individual to another private individual. Apparently that worked for Customs on both ends, but no doubt any shipping company can give you advice or a template to fill out.
Reinier