First of all, don’t hesitate to go to their websites and compare rates using online calculators, as all three of them obviously have some advantages and disadvantages. So, let’s try to compare them based on the type of item you’re about to send.
Less than 2 lbs / more than 2 lbs:
If your item weighs less than 2 pounds, it will be cheaper to use USPS, but be aware that it especially applies to smaller packages (up to 13 oz) that can be mailed via First Class. As the weight comes closer to 2 lbs, USPS pretty much loses its advantage. Also, according to many small business owners, USPS is less reliable, even though it’s cheaper. So, it’s up to you to decide what’s more important for your business: money saving or reliability. It’s a shame that sometimes you just can’t have both.
Next Day Delivery Service…
USPS Express seems like the cheapest option, but there is a small pitfall: sometimes the actual delivery window is 2 days, and the only way of knowing it is to check online. Basically, they guarantee to deliver on time, but in reality, they simply offer a refund for late deliveries. Again, it’s up to you to decide whether timely delivery is a priority. Also, USPS doesn’t offer morning deliveries. Thus, you may lose a potential customer who needs to get his parcel in the morning hours.
2 to 3 days window…
FedEx and UPS guarantee their delivery times, but you obviously do have to pay for it: they are significantly more expensive than USPS (sometimes it even costs twice as much). USPS is cheaper but they don’t guarantee their delivery times for Priority and First Class Mail. 2-3 days is a typical time, but it could vary depending on many different factors that you can’t foresee or control.
Conclusion
If your store mainly ships items that are under 2 lbs, USPS is probably the cheapest carrier (in most cases), but it can also be less reliable, as packages are often delayed or get get lost in the mail. UPS and FedEx, on the other hand, can be more expensive, but as they are competing, privately owned carriers, their healthy competition results in increased reliability for us, customers.
UPS Ground and FedEx are the cheapest options for heavier items (2lbs or more), provided that your clients are not in a rush to receive it.
The bottom-line is: Tight deadline and/or large item – use UPS or FedEx. Tight budget and small item – use USPS.