Well, I'm going to go against the conventional wisdom here... I'm actually a fan of USPS, and will opt for it over UPS or FedEx ground if I'm given the choice - I find it's faster and generally much cheaper. And they deliver on Saturday (though I expect that might be something that goes away sometime in the next few years as a cost cutting measure).
However, I'll admit that I don't expect their tracking for non-express packages to be of much use (maybe the the tracking is helpful if a shipment gets lost?), and I certainly can't say what their international shipping record might be like.