One with no fees, or limits.
The big oil stations here that offer such cards are .08-.10 or more per gal than where I buy it.
Like right now, I filled up today @ 4.19 down the road at Chevron 4.35, Shell about the same, Exxon a little cheaper about 4.32
So I guess it would depend on the rebate, fees, and pump price.
BTW, alot of those cards offer a tease rebate rate.
And if you are talking about just a standard CC... Make dead sure you are not an min late ever on the bill.
Late charges, and interest will kill any savings.