I've owned over 30 bikes in my over-30 years of riding and the one I probably miss the most was easily the least interesting and certainly the slowest.
WHY I BOUGHT IT: Because the '82 Suzuki GS450E was the only new bike of reasonable displacement that I could learn to ride, not get bored of 50 yards from the driveway, and afford.
WHY I SOLD IT: Apparently it wasn't reasonable enough displacement wise. I bought a used 1980 CB750F to replace it.
WHY I WISH I HADN'T SOLD IT: It was my first bike, so it's the one that tugs most at my heart. It was also my first loan—$1500 out the door. Here I am in 1982, proudly astride my brand new little inline two-banger Suzuki GS450E. An added bonus was that brown suede Members Only jacket that I believe wasn't even cool back then.