The Cap One card is pretty much like a "cash rebate" card where "miles" accumulate and they are worth dollar amounts off travel. If you are having problems redeeming miles through Delta, you can always select a different miles card through an airline of your choice. If you want the flexibility to choose which airline you want to fly, you can consider Diners Club (transfer into almost any airline), an Amex Card with Membership Rewards (limited airlines), or the Starwood Amex Card (transfer *wood points into airlines miles with no fee plus a 5,000 mile bonus for each 20k transfer). This way you can find award availability for each reward and then transfer miles into that program to redeem.

You may also want to look into Citibank's PremierPass line of credit cards, which offers airline redemption through their travel partner. This is a fairly new card and card members who have redeemed for flight have had a mixed experience with flexibility. The plus with the PremierPass is that points add up pretty quickly and you get "FlightPoints" for ticket purchases. You will want to look at the threads for each individual card product to see which one best suit your needs. Hopefully I have offered a glimpse into what you can expect.