Adam Warshaw has dealt thoughtfully with this exact topic in his blog:
Why Mantle? - Adam's Card Blog
Overall though when it comes to cards in general I'll make two points:
1. Rookie cards are tremendously overrated and thus overpriced. I'm more interested in a player's most aesthetically pleasing card than in his rookie card.
2. Unmarked checklists are tougher and thus more exciting to find than are any stars.
