Actually, these two have a bit more diffrent from each other then the previous games. Do some research. Which pokemon on the front cover interests you more? Black has Black city, white has white forest. BC is more about battling trainers, where as WF is more about capturing wild pokes. also be aware of the game specifics. you can only catch certain pokes in each game. there are other diffrences, mainly cosmetic tho like in this one town, cant recall which, in one its more tech looking in the other its more rustic. its all preferance tho as stated you can trade for the game specifics. look here for more info
http://www.serebii.net/blackwhite/exclusives.shtml
http://www.serebii.net/blackwhite/versioncity.shtml