Man i love the card game (best mini game ever, and YES still with the plus/same/same wall rule). I actually discovered a foolproof strategy card layout with the following cards (and obtainable pretty much at the start of the game). The cards you need are as follows:

(a) Zell
(b) Quistis
(c) Diablos
(d) Mini Mog
(e) Ifrit

It would only work if if you started the game first. It would work as follows:

[Diablos #1][Computer Card #1][Quistis #2]
[][Computer Card #2][]
[][Ifrit #3][]

...And then either way you would beat them with the Mini Mog or Zell card in each of the remaining slots. Try it out, it's sure to work.