Finally, look at which path allows you to change later...in other words, is it easier to become a pilot and then transfer to be a Marine, or the other way around. I would bet that if you turn down a pilot slot now, that you will not EVER be offered it again, no matter what you do. On the other hand, unless the Marines have very strict age requirements, if you don't make it through flying training or you decide it's not for you, you can flow into the Marines if you can meet the physical requirements.
Either way, good luck, man up, and no regrets. Oh, and once you turn 18 (or whatever age it is in your country), it doesn't matter what your parents think. What matters is what you can live with. If you live your life based on other people's wants or expectations, you will NEVER be happy.
FC