As it asked. Which ones do you prefer?

I've worked for UPS.... soo.... i gotta go with them

LOL. Conflict of interest.

Does anyone know which one has been around longer? Just curious and too lazy to research.

With the exception of usps, because I'm sure they have been around longer.

I think it depends on which country the pacage is beign handled in. DHL is great in Italy.

Domestic (US) to government P.O. Boxes
USPS we went with them - was there in 2 days, no problems and I think most will tell you the same.
IMHO the other express couriers are fine, but waste of money when USPS gets it there just as fast or faster.

Overseas delivery
Only speaking for US to Germany; it may very well be different in other countries - DHL is the way we go - its a tad (maybe $7-$10) more than USPS, but since DHL is also the Deutsche Post, theres not a lot issues (there are other reasons DHL is good too, as they have good results in many other countries too).

I've never had a problem with USPS with domestic stuff. USPS to Tanzania used to be reliable/reasonably fast (2 weeks), but now it seems to have slowed down a bit. It took me 3.5 weeks to receive the package my mom sent me while I was there. And now, Ombeni has yet to receive the letter I sent him three weeks ago, but I've already received things that he sent me a week and a half ago. Maybe that just means the Tanzanian post offices are slow at sorting mail... I dunno!

We did AOS with USPS, it took less than 24 hours (regular mail), no complaints there.

They're understaffed here in NM though, so mail can take awhile. So we FedExed the I-751.

FedEx, I work for them and get a 75% discount.

USPS

Well, the US Postal Service was around before any of the others.

UPS came along as an alternative to US Postal specializing in delivering parcels.

DHL actually came along before FedEx, although I think most of us heard about FedEx first.

FedEx was the first overnight guaranteed express carrier with a focus on moving packages by air. If memory serves me, they originally only moved documents. Their founder was retired US military and the original business concepts were based on a tightly regimented military style of precision and control.

I prefer FedEx, very reliable.

USPS uses more and more automated processing, optical character readers that can read handwriting. The majority of the domestic mailpieces are not looked at by a human eye until they reach the destination zip code, and often not until they reach the actual mail carrier. This has resulted in a dramatic increase in efficiency for domestic mail, but for a country with a five-digit postal code, this can result in mail being misdirected to the U.S. zip that's identical to the foreign postal code (for example, mail destined for Spain being sent to South Carolina, which can mean a three or four day delay), but I don't think Tanzania uses postal codes (??). Writing the name of the country in large caps on the last line of the address, and the foreign postal code in a smaller font on a previous line, can help speed things up. Sometimes, the only thing that stops the foreign mail from looping back to the wrong U.S. zip is a line drawn through the foreign postal code so the OCR overlooks it. But then a human eye will have to read the postal code once it gets overseas if it's lined through, so the speed at that point depends on whether a human or a machine is sorting it.

I have one question for those who knows.

Which services guarantees that the mail will be delivered properly in another country? Give me your input, possibly some proof if possible.

FedEx

USPS priority mail with delivery-confirmation would be choice #1 (economical, yet fairly quick).

DHL good for sending overseas (as I had to do about an RFE).

FedEx good for domestic (or to-Canada) deliveries.

Used DHL between 3 locations: Indonesia - the Netherlands - US. No complaints so far.

Sending stuff inside the US....I like USPS
Sending stuff outside the US...I like FEDEX

They hsve never failed me yet

Too bad fedex isn't available in my country.

UPS but internationally all $$$$$$ bcp