Well-then-there-now...
...what a question! I'd have to say Hoover's first washer - the 0307(?) I love it's simplicity and stylish compact-ness. And as always, 'the older, the better' is the general rule for my collection! I do like the original Keymatic, too - they're quirky enough in form and function to hold my interest.
But we shouldn't be talking about this! SHHH, my parents will hear, and they'll be after your blood if you start me collecting washers as well - we've already got vacs coming out of our ears!
Paul - thanks, glad you like the videos! Yes, I'd never used the Lux 170 before, but I was quite impressed - a bit modern for my collection, but it was fun to play with! We've always been a Hoover-upright family, since my great-grandparents bought their first vac in 1935. True to form, my collection must be 85% Hoover!