Aggressive XC is just xc of old imo. XC has become a dumbed down offroad race to the point where road bikes can win competitions. (this is my opinion from having watch many WC races and even some state based ones...they are pretty none technical) Agressive xc is what I think of the guys in the early 90's doing. Jumps, small drops, rock gardens. Instead of avoiding technical terrain they work with the terrain to make a fun course.
Are you interested in a dually or a hardtail?