From my experience, whether it is NBA, NFL, or NHL cards, the most valuable cards are the rookie cards with more value for rookie cards of superstars than for common players. I've personally found that Beckett provides the best estimate of card values.
Depends on the player and age of the card. Rookie cards of popular players tend to be the most valuable, especially if they are older players. Autographed cards as well as the game used cards of popular players are worth a good deal. Inserts are worth more than cards from a basic set.
The most valuable basketball cards has to be Upper Deck Exquisite from 2003-2004. This set contains Lebron James Rookie Autographed Patch card which is worth about ten thousand dollars.
The older the cards the more valuable they are. Rookie cards such as Michael Jordan or Magic Johnson are worth more than a bench player. Certain cards are also made special determining the edition of the cards. If the card is signatured by the player himself, the value increases a lot.