If the Heritage/84 had a nicer looking belt lifter, I think it would be my favorite. The sticker on them is boring, other than that I love how the machine looks with the thicker bag (over the Tradition and previous cloth bags). I like the solid bag holder as well compared to the flimsy wire type on the older machines.
But my vote probably goes to the Tradition, love the color scheme and the shiny belt lifter. I just with it had the same style headlight hood as the Classic/CIII those were stylish!
I love the 500 and Sanitronics but they don't have anywhere near the cleaning power as the "Classic" Kirbys. (Although it will be interesting to see how my Sanitronic VII will perform with a HEPA bag and ball bearing roller brush.) 
