Stanford Wong's BJEdge program puts the house advantage for 6 decks and stand on soft 17 at .41%, while the 2-deck game with the dealer hitting soft 17 is .40%. So the two are nearly identical.
However, for most recreational players the 2-deck game is better, since you will play fewer hands per hour. Even though the .4% casino edge is low, it's still negative, so playing fewer hands means losing less (you play fewer hands per hour because there's more down time for shuffling on a hand-held game).
Stanford Wong's BJEdge software gives the house edge for nearly any blackjack game you find. It's available from the ShopLVA catalog.
