Marine Corps or Navy

I am interested in pursuing a career in the Navy or Marine Corps,
quite possibly as an Aviation officer. I recently met with a former
Army officer, and he was telling me about parts of a military career
that I didn't know about. For example, he mentioned that you can
become a "military attache" in another country. He also mentioned
embassy duties and working in the Pentagon. How hard are these kind of
tours to get? Is there a difference Navy vs. Marines?

My other question was, in your experience, do the Naval Academy grads
fly up the ranks faster than the NROTC guys (or OCS)?

I'm not fit enough to be a Marine right now, but if I decide I want to
go down that path, I will start to get into shape. Any other things
that I should think about? My reason for asking is I need to check the
Marine or Navy box on the NROTC application, and if I feel like I want
to be a Marine, a few other important college options would open up
for me.

Thanks!