As far as which is easier to learn, that depends on you, like Cent said.
I think front flips are easier to practice OUTSIDE of a padded gym area, because once you get the general technique down, they won't hurt you too much on the grass or sand. I just got the front flip in the gym Saturday and I'm gonna work on it in the sand pit this week.
Backflip, on the otherhand, I still have to practice in the gym.