KH1, Chain of Memories or Re:Com, KH2, and BBS in that order.
Days is pretty unimportant unless you're a huge Org. XIII fan, and Re:Coded's impact on the plot is limited to the short ending scene after you beat the game.
Hell you don't even HAVE to play CoM before KH2. I didn't, but when I went back and played it, it did make some parts of the plot easier to understand.
--
http://img.imgcake.com/AitchDeeTee/panicdancegifta.gif
http://backloggery.com/herodeltiempo/sig.gif