For small items, Use PayPal to send First Class.
When possible, use USPS Priority, because it is often cheaper than the rest.
UPS is a joke. Seriously. The online label creation sucks, and the billing sucks too. Not to mention the fact those crooks still owe me like $150 that I will never see again.
The best thing to do, it setup a business account with FedEx. Ask to speak with a Sales Representative about special pricing. When he calls you back, talk up a storm about how you use UPS and USPS right now, but would prefer to use them instead. Unfortunately, the prices are higher than what you already pay, so you really need a discount to start with, so that you can justify the transition. If you do it right, they will low ball everyone else, and you can use them for everything. The billing is automatic, and the shipping label creation is a breeze.