have owned, R6, ZX7, Buell S-1, multiple Harley big twins and sportsters, a Vrod, two Suzuki s40's, Cb360, kz200, tu250x, Kawasaki 454 ltd, z125 pro, Ducati 620 Monster and a bunch of cb125,175 and 350-4's. The R6 was smooth but with all your weight on your hands, what vibration there was, soaked right in.
Two smoothest at speed were the Buell and my Rebel, almost electric feeling.
I just like simple things, bit of a minimalist I suppose, and for example a valve adjustment would not even require removing the tank. four valves to adjust vs eight.