Depends on the weight.
Under 4 lbs First Class, Over 4 lbs Priority, The Flat-Rates boxes can be good in some circumstances but they have never worked for me.
Keep in mind that the International flat-rate boxes have much lower weight limitations than the domestic (US) boxes.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
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