Searching for the Heart of the cards

[PuPu]

If you want just plain old card duels, then YGO: The Eternal Duelist Soul. There's no story or anything except duel, get better cards, duel.

If you want the best YGO game currently out (or so I hear) YGO 5D's Stardust Accelerator.

If you want a really, impossibly tough to beat YGO game, YGO: Forbidden Memories. No seriously, don't get this. Unless you enjoy grinding for hours and hours to get good cards only to realize that the COM will always have better cards which are impossible for you to acquire.

edit:

hours and hours

This is actually REALLY inaccurate. It should have said "weeks and weeks" and that's assuming you are REALLY lucky and play nonstop. "A few months" is actually what will most likely occur before you actually get the minimal cards necessary to win the game.