:3 BBS is probably the best one to start with aside from KH1 since it's a prequel to the whole series. You don't really need any background knowledge like you would with the other games. It also happens to be my favourite, so go for it!
Hey friend, I was totally asking 'cause you seem to be knowledgeable in this field, but I'm trying to get into Kingdom Hearts, and right now I can only get access to BBS. I can get the others, but is this a good one to start with?