The Gnat had true swept wing handling, a very responsive engine, an excellent offset TACAN system, was easily supersonic in a dive and had a superb compass system. You also felt that you were part of the little jet when you strapped into the simple, reliable Folland seat.
The Hawk had none of the above. Yes, it was much easier to fly, known as the JP6 by some, had much better range and had simpler systems. I can well believe, beardy, that it received a less-than-complimentary assessment from an RAF TP! I also recall reading in some Learning Command crash comic "The deficiencies of the Hawk compass system were well-known before the aircraft entered service".... So why was it allowed to enter service then? I only flew the 'orange button' pre-AHARS Hawk and the compass system was utterly dire. The Hawk had a better radio fit, with both UHF and VHF, whereas the Gnat was single UHF-only, with a 243.0/243.8 standby radio. The Hawk also had a full-frequency ILS system (but no VOR), whereas the Gnat had a 12(?) channel crystal system which could only be reached by someone with the dexterity of James Herriot sticking his hand up a cow's arse.
The worst aspect of the Gnat was its twitchiness in close formation - which was a bugger. Whereas despite its sluggish engine response, formation in the Hawk was dead easy. I once left 1 notch of flap down (by mistake) when flying the Gnat in close formation and it was vastly easier to fly - interesting that the Reds usually flew it that way!
At TWU, the Hawks I flew didn't have the dorsal fin extension, so weren't terribly yaw stable for strafe. Astonishingly, they also lacked a gun sight as good as the ones we had in the Hunter a few years earlier. But they did have a much better camera - no juggling with cine mags unlike in the Hunter.
The Gnat's longitudinal control system was very complicated and failure procedures had to be immediate and correct; AC/DC failure was also quite complicated to resolve. STUPRECCC and CUBSTUNT probably haunt many an ex-Gnat pilot to this very day! By the time I flew it in 1975, the Gnat had a feel trim position indicator and Mod399 standby TPI changeover switches, which made the hydraulic failure procedure much simpler and safer.
But my favourite red-and-white trainer? The lovely Hunter GT6 - and not just because it didn't have a seat for a QFI. Quite viceless and it went like stink!
That said, one of my favourite Hawk trips ever was a 2-ship tactical formation exercise at low level in Devon, led by sharpend - quite brilliant fun!