Used different couriers over the years and the two that, for me at least, stand out are Fedex (when sending to the USA) and DHL. Excellent tracking info and very quick. OK it may cost a few quid extra but that more than makes up for the service received.
Having bought quite a number of pens over the years from overseas, I share with you my experience with mail and courier services:
1) Packages with tracking numbers from most countries which enter the USA through the USPS pass through Customs efficiently and never result in the payment of duty. Never.
2) Packages coming from Italy or France -- whether sent by registered mail or colissimo or the local equivalent -- are always delayed at least 10 days in Customs on the US side. There must be a reason for this.
3) Packages that are sent via DHL always, without fail, are delayed in Customs and always, again without fail, involve the payment of duty. This has been my experience over the past 10 years. If I find out that a package is sent by a local courier which has a partnering arrangement with DHL, I literally cringe. I refuse to use DHL any longer because of this.
4) Packages that are sent via FedEx involve payment of duty about 50% of the time. One package was actually delayed in Customs for 10 days because the airway bill said "fountain pen" and Customs wanted to know if the pen had ink in it, because if it had ink, the ink could not come into the country unless accompanied by a declaration from the shipper that the ink was not made of a toxic substance.
5) The most efficient and the cheapest courier service in the world is EMS Japan. It has no equal. It always passes through Customs quickly and without any hiccups at all. If only all courier and mail services were like it, the world would be a better place.
6) I have had three experiences with Hong Kong's EMS equivalent, and they were all delayed in excess of 8 days in reaching me.
7) UPS from Europe is amazingly efficient (I have received pens from Madrid in less than 24 hours). UPS Ground in the US is the slowest service there is, followed by FedEx Ground.
8) Do not under any circumstances ever use Aramex from the Middle East. They are slow and all packages, every single one, is opened and manhandled. I have also had things stolen, and they refused to compensate me. One was a rosary that was included in a package with a fountain pen (one wonders who would steal a rosary, but ...).
Again, these are my experiences, but I have quite a lengthy track record, and I am wondering whether others have had the same experience.