It shouldn't be either of those, and yet both. Aggressiveness refers specifically to how much a razor exposes the blade to you -- essentially how narrowly or widely it guards the blade. A more aggressive razor will expose the blade more, while a milder razor will expose it less. Whether you experience that exposure as a smooth, close shave or a rough, uncomfortable one isn't inherent to the razor, but is down to other things like your face, your mood, or your technique.
It's entirely possible for someone to consistently get a closer shave from a milder "razor X" than a more aggressive "razor Y," but that doesn't make razor X "aggressive." It just means that it's a more natural fit for them than razor Y.
Spot on , Porter. To me, the term has always been an objective one about the amount of blade exposure. One's response to that exposure is a completely different matter, and really nothing to do with the term.