short distance and lightweight always use USPS.... especially when dealing with a residence...... if long distance and you can fit it in a USPS flat rate box that is the way to go.
If using UPS, create yourself an account and make your own labels...if you are off on weight I think UPS will adjust..... problem is UPS "stores" ...... they charge more, not sure if there are any limits on them, but I think it they tend to charge shipping costs and whatever profit they want...
those are the only 2 companies I really use