I personally think the Aegis is a better knife than the Flash, but both are good knives.
Both the Flash and Aegis have the same handle material and do not have liners, so pretty much a wash there for comparison sake.
They both have the same AUS8 blade steel, Assisted opening mechanism, and reversible pocket clip.
For the the difference comes from the shape of the handle and the blade design. The handle just seems to fit better in my hand and I like the larger blade size offered by the Aegis.