Kazmir is worth more than Cain just for being a lefty, but if Cain makes it to the same level he will be a better draft. Kazmir was a top 5 pick talent, though he fell about 10 spots to the Mets because Morad wanted a very hefty signing bonus, while Cain didn't have much buzz.
There's actually a chance that Cain could top out higher- Kazmir is attracting a lot of comment to the effect that he may end up a closer rather than a starter because of his body type. If Cain tops out as a top/middle rotation starter, he's bviously worth more in the end, though Kazmir may be almost unhittable as a closer.