There are several factors to consider when choosing a common carrier for shipping a guitar—

• Shipping cost.
• Convenience: Are driver pickups available at your home or workshop?  Or if not, is there a fully authorized distribution center—not just a drop-off location—within reasonable driving distance?
• Package insurance: Your guitar is most likely a high-value item, so the cost of insuring it and any value limitations on contents are crucial.  If you’re shipping a high-end guitar by ground service, insurance will be by far the largest cost.
• Air or ground shipment: Air shipment with any in-transit time option is much more expensive than ground…as much as 4.5x more for 2-day air, even more for overnight.

These are the most commonly used options available to guitarists and luthiers for shipping a guitar—

• Federal Express (FedEx)—Fedex is a reliable, easily accessible shipping service; I have shipped many guitars via Fedex over the years.  Online shipment creation, including pickup and payment, is available if you have an online account; otherwise you will need to convey it to an authorized distribution center.  The Fedex 2015 contents insurance rate is $0.90/$100 over the first $100.  There’s just one hitch with Fedex: If the guitar you plan to ship is more than 25 years old, you can only insure it’s value up to $1,000.  I would recommend Fedex for shipping new guitars, especially if you anticipate warm weather anywhere along the ground route…their trucks are white and therefore heat-reflective.
• United Parcel Service (UPS)—Shipping with UPS is similar to FedEx with two exceptions: receipts and insurance.  UPS will insure shipments of high-value guitars regardless of age.  However, if the guitar’s value is more than $1,000 and the shipment transaction is done online by an account holder, two copies of a special receipt are required; both are to be signed by the driver on pickup, one for the account holder to verify the pickup, the other retained by the driver for UPS records.  If the guitar is brought to an authorized distribution center, the receipt provided there is sufficient if an insurance claim needs to be filed later.  UPS is normally my shipper of choice.
• UPS Store—UPS Stores can be helpful resources for many purposes…but maybe not for shipping a guitar, at least not the actual shipping of it.  However, if you’re an inexperienced shipper and are uncertain about packaging a high-end guitar, you may want to take it to your nearest UPS Store and let someone there do the packaging for you.  You can then bring the package to a UPS—or for that matter a FedEx—distribution center for actual shipping.  UPS Stores are independent franchises, so their prices and services vary from store to store.  My local Store will accept guitars packaged by a sender for drop-off but will insure only $1,000 maximum value, so that’s not a good option; if one lets the Store do it all—packaging, payment, the entire shipping transaction—they will insure for full value, but their insurance rate may be up to 2.5x the rate for a distribution-center transaction, so taking the package to a distribution center (UPS or Fedex) for shipment may be worth the trouble.
• U. S. Postal Service (USPS)—It is possible to ship a high-end guitar via USPS…but not too high-end: USPS declared-value is limited to $5,000 for any service; what’s more, their insurance rate is 1.5x+ that charged by FedEx and UPS when shipping from a distribution center.  That’s why I’ll probably continue to turn to USPS for convenience when shipping small items—they’ll pick them up right out of my semi-rural mailbox, no pickup charge—but probably will never ship a guitar that way.