The EV of blackjack varies depending on rules and number of decks (the fewer decks the better, rules being equal). Most games that you will find in a casino are -EV, usually between -0.2% and -1%. However, sometimes promotions or casino errors will make a game +EV.
Rules to avoid:
Short pay blackjacks (6:5 is horrible)
Dealer hits soft 17.
Any restrictions on doubling (double 10 and 11 only, etc.)
No double after split.
Rules to look for
2:1 blackjack (very rare. Sometimes a suited blackjack or some other subset will pay 2:1. This is good if it's not offset by bad rules)
Early surrender: Also quite rare. Early surrender means you can surrender before the dealer checks for blackjack. It will usually make the game +EV, unless offset by other really nasty rules. Significant strategy changes are required to take full advantage (you surrender a lot of hands against a dealer ace)
Dealer stands on all 17's.
Double after split.
Late surrender: This is the common form. You can't surrender vs. dealer blackjack. Surrender 15 vs. 10 and 16 vs. 9, 10, A.
Note that changes in rules and number of decks change basic strategy consult
Wizard of Odds or
blackjackinfo for correct strategy.