You can choose either whichever is giving you better rate. No need to use a box. The case dear
@maverick1982 has mentioned is true, however it happened because I think the package was sent to a PO box address and UPS couldn't deliver it and the package got lost on return as they messed up the return unit number.
However, since then IRCC has updated its PPR instructions and they themselves include street address for US residents. So it should not be an issue now.
And you are correct. For Fedex you will need to generate commercial invoice but you don't need any extra effort for that. The system automatically generates it.
For UPS, there is an option where you mark it as personal documents and it doesn't generate commercial invoices and it works fine. I haven't used it personally though.