Tough to say
I don't really find myself yearning for a particular machine, although there are a few I had or that were in my family that I sometimes wish I had back:
• My grandmother's 1977 vintage orange Eureka Princess with matching power nozzle. It was my main machine from about 1996-2003. Its ignoble fate is well documented elsewhere on this site and I won't bore you with the details again. Still, I have an inordinate sense of loss regarding this machine and I don't understand why.
• My parents' pink and gray Lewyt canister. We used it until the hose fell apart but the machine itself never quit. I've never seen another one exactly like it and I doubt I ever will.
• My grandparents' Electrolux. I think it was an LXI. It was in use in their house for as long as I can remember. It was probably still in the hall closet when I last set foot in there after my grandfather's funeral in 2001. Although long gone now, it's probably why I gravitate toward Electroluxes and have a 1205 and a Super J today.
• My Kirby Heritage 1HD. My most recent ex-girlfriend "borrowed" it three years ago, promptly pitched her Oreck in the dumpster and never gave it back. This would probably be the easiest of the lot to replace, but I guess you could say I've already replaced it with either the G5 or the Gsix I picked up last year, or knowing my personality, maybe both.
I'm not actively on the hunt for any of these machines; I've got too many vacuum cleaners as it is. But if the opportunity to acquire one in nice shape for a good price were to arise, well then we'd just have to see, wouldn't we?