Assassins Creed vs Assassins Creed II?

I would suggest playing AC1 first. It's not the best out of the two (although I still love it and I love Altair the most!) but I played AC2 first and because of that I didn't understand the story fully. D: It also had some spoilers. I now wish I played AC1 first. Really, you should do what you feel is best though.