PayPal account - advice - credit card or direct checking account as default?

Situation: From time to time, I buy stuff on Ebay and sell stuff on Ebay. PayPal seems to be the default choice (and to be fair, the easiest choice) for handling money both coming and going.

PayPal gives lets you have multiple sources of funding (and receiving money) tied to a PayPal account. In my case, I have a checking account and credit card associated. You have to choose a default – which PayPal sets to checking account, since it costs them less (ACH debit versus the 3% they are charged by the credit processors). Herein lies my question.

Checking account advantage:
– easy, direct transaction. Fastest way to close out a buy or sell
Checking account disadvantage:
– a third party has direct access using ACH and can put through unauthorized debits (although theoretically PayPal protects you)

Credit card advantages:
– put off payment for a month
– better protections if you are cheated
Credit card disadvantages
– length of time between purchase and payment
– not sure if there are any others

So what should I select as my default payment / credit method?