live things such as fish and plants I would only ship usps since its wayyyyy cheaper and 2-3 day arrival is guaranteed (well most of the time)
For other things that are heavy (non living) then ups works out well since their rates for heavier items seem to be way lower than usps..
I disagree. Slightly anyway. USPS has the Flat Rate boxes. You can ship up to 70 lbs in a 12x12x5" box 2-3 day priority for $12.95. Larger heavier items may be cheaper elsewhere though. IDK.