BWI. Real close to the Academy. sometimes they have people to escort you back to annapolis and if not you can grab a cab or bus and be there in 30 minutes.
I've gone midstore parking lot to BWI drop off in 18 minutes. You can't get to National that fast. You'd be hard pressed to get to New Carrollton that quickly.
It has been my observation that Admissions, at least, tends to favor BWI over the others; generally when it arranges transportation it is to BWI. For what it's worth.