With Coinbase, you’re buying directly from Coinbase the company at market value. On Coinbase Pro, it takes a while to match your request to another buyer/seller.
I would suggest to use pro at any time Coinbase pro fee is $6 for 1 ETH purchase,where Coinbase fee is $44.64
You are placing an auction on pro that must be fulfilled by the other side, whereas coinbase executes the order at a higher price to guarantee the whole thing goes through instantaneously
Coinbase pro -probably limit order price executed ,Coinbase always execute market order price