Here are the service levels for three of our most commonly-used carriers:
USPS:
First-Class Package/Mail Parcel (max 15.9 oz)
First Class Package International Service
Priority Mail Express
Priority Mail Express International
Priority Mail
Priority Mail International
Parcel Select (USPS ground)
Note: The USPS technology (ePostage) used by Shippo does not currently support the use of Media Mail, Library Mail, First Class Flats, or Letter Rates.
Fedex:
Economy
2 Day
Standard Overnight
First Overnight
Priority Overnight
Home Delivery (same service as Ground, but for deliveries to residential addresses)
Ground (same service as Home Delivery, but for deliveries to business addresses)
International
International First
International Priority
Express Saver
3 Day Freight
2 Day A.M.
Smart Post
UPS:
Express
Express Early A.M.
Ground
Mail Innovations Domestic
Next Day Air
Next Day Air Early A.M.
Next Day Air Saver
Saver
Second Day Air
Second Day Air A.M.
Standard
Three-Day Select
World Wide Saver
Worldwide Expedited
Worldwide Express
Worldwide Express Plus