There's quite a lot that goes into answering this question. The fees for swipe, chip, and contactless transactions are almost the same (Square charges 2.6% + 10¢, while PayPal charges 2.7%). Keyed-in transactions are identical, as are ecommerce sales.
However, PayPal charges extra for non-US cards, charges you the original transaction fee for refunds, and charges $20 for chargebacks.
All told, Square might just come out a little bit cheaper. Plus, Square's POS platform is stronger than PayPal Here.