I use three different cards.
GM M/C pays 5% on all purchases. "Rebate" is actually applicable only to a new GM car purchase. Max is $500/year so when we reach that, we switch to a different card. So far lifetime on that card we have redeemed over $5,000 and currently have about $2,300 in earnings applicable to next car purchase. When you consider the interest charges on a car loan, the current $2,300 is actually worth more since it reduces the loan balance, saving several hundred dollars in interest.
2nd is BP gas. 5% rebate on BP gasoline purchases, 2% on Travel and Dining, and 1% on everything else. Can redeem as either (1)BP gift card, (2)Check paid to yourself, (3)Contribute to a fund
3rd is Disney Visa. Basically 1% in Disney Dollars. We use this card, swapping with the BP card, when the purchase will only be at 1% anyway, and we've maxed out the annual rebate allowed toward the GM card.
Of course, never carry a balance over for any month or the CC interest wipes out any advantage to having a rebate. We always pay the full balance every month.