The game uses Steamworks, so it has to be activated on Steam no matter where you purchase it from.
Once you buy it from BestBuy, you’ll get a cd key that needs to be activated on Steam.
I’ve never purchased any digital games from BestBuy yet, so I can’t comment on their service. I can recommend buying this because you can just activate the game directly on Steam.
They also had a great deal on Arkham City yesterday but I’m waiting for more feedback on their digital distribution service before I post their deals.