My first fighter, the North American F-100. I specified the builder because there are several 100s, but only one Hun. In 400 hours, it and some squadron pilots taught me more about flying than 10,000 hours anywhere else could have--basic handling stuff.
The C-5, of course. A nightmare to get out of the parking spot--truly a maintainer's full employment program, but could carry many things that couldn't be flown on anything else and a pleasure once airborne. Running a 10-man crew taught me a thing or two about herding cats, as a side bonus. BTW, funny happenstance, I flew both F-100s and a C-5 to the Boneyard.
The Global Express, my current steed. 12 hours at M.84, a reliable magic carpet. Flies beautifully, but few modern planes don't. Can't wait for the new cockpit.
Along the way, the A-10 was fun and challenging until the silk letdown, the Citation was a pleasant entry into corporate flying, the Sabreliner another pleasant NAA flying machine, if cramped in the cabin. Being an engineer on Mr Boeing's 727 was boring were it not for all the entertainment provided by Apollo 8's commander.
In short, I loved 'em all.
GF