UPS is the biggest and the most reliable mail carrier in US. Those who who ship items withing US and do not wont to spoil their reputation only use UPS. USPS have too many issues with stolen packages and non-delivery. 85% of apparel and footwear is being delivered via UPS. Their API is one of the most documented.
May 14, 2015
Thanks for Amantay.
You are right, it'll be useful Addon.
For a while, we are waiting for user votes to speed up the implementation.