Mileage certainly varies from area to area! Regarding UPS vs USPS, I'll opt for USPS for international (US to Canada anyway) purchases every time. UPS will charge the crap out it with "handling and brokerage" fees, even if its made in the USA and duty exempt!
FedEx seems to have navigational issues. Last year I ordered a set of custom window blinds from a "Canadian" company owned by a US company- no problems, they do good work at a good price and I don't have to deal with cross border issues. After about 2-3 weeks nothing has shown up so I phone "customer service" and ask about my order. Guy says oh, it was delivered to (some address), Winnipeg, Manitoba. I'm in Whitehorse, Yukon. I say that's not my address and he asks maybe it got delivered to a neighbourhood one over from mine. I ask him where he is and the reply is Houston, TX. I laughing said well, if you ordered something from New York to Houston and they delivered it to Seattle, is that one neighbourhood over? He laughed and said I'll get that fixed for you right away. Had the blinds in a week.
Good company service, questionable delivery service! lol