Answer by Thomas Zerbarini:
When we talk about maneuverability in an aircraft you have to consider that an aircraft is more maneuverable the more its aerodynamics are "unstable." The aircraft I would say was the most maneuverable would be the experimental Grumman X-29 flown by NASA:
This unusual looking aircraft that appeared to seem it was flying backwards was so unstable that it required a triple redundant Fly-by-wire () flight control system to provide "artificial" stability and keep the aircraft from spinning out of control. The cockpit was simple yet the aircraft was ahead of its time.
The aircrafts instability was inherent in turning the wing backwards. The aircraft wanted to pitch, roll and dutch roll violently if not actively controlled by the triple redundant fly-by-wire systems with an analog back-up.
I'm certain that the variable exhaust nozzles, being used in our most advanced fighters today, if placed on an forward swept design like the X-29 would have dazzled NASA and the Pentagon on the extreme maneuverability of such a concept.
You'll have to consider that todays designs are larger demand multi-role tactical fighters that are bigger, use stealth technology an
d would have a tendency to be more lumbering in a dogfight than say the F-16 or a design like the X-29.
In an effort to save money, congress tends to like the multi-role fighter platform. Such a platform depends more on technology, missiles and radar to defeat a foe and the aircraft tend to be larger and more lumbering.
This idea has happened in the past with other aircraft like the F-4 Phantom. A huge powerful aircraft that was too big to effectively dogfight with lighter more maneuverable fighter jets. We may again see another aircraft surface that is light and nimble to truly replace the F-16.