Re: the 1205
I would say that any "iteration" of the 1205 is a good one.
In 1968, when the 1205 FIRST came out, it was still a few months before the Consolidated Foods takeover. It had the 535 watt Model G motor, and it came with a pigtail connector for the power nozzle (before the introduction of the fully electric hose). The 535 watt motor is essentially the same motor that the Model G, Model L, Model F Automatic, Model R, Model S, and Model E had. (Actually, some of you may not know this...but the Model L was LABELLED as having a 535 watt motor, however, both my '67 and '74 Ls both draw around 590 watts as registered on my Kill-A-Watt power usage meter).
I'm not sure exactly when the motor in the 1205 was upgraded after the Consolidated takeover...but all 1205s had very reliable motors. Additionally, since the later models (the Super J, Olympia, and Silverado) had the same body dimensions, the motors for all these machines were interchangeable.
I would say that if you find any 1205 in really nice shape, it would be worth the investment. I would like to have a 1205 myself; however, it's a bigger machine than I think I could easily navigate around my tiny apartment. I like the smaller economy models for cleaning here...they're easier to maneuver and use on the carpeted stairs I have that lead up here (and need to be vacuumed once a week).
The Model 1205 was certainly a popular model, and although they still are a dime-a-dozen after almost 40 years, many of them are in very poor shape from years of use and abuse. But every so often, I will see one on eBay that looks like it was hardly ever used. Oftentimes these pristine ones are found at estate sales, where the wealthy inhabitants of the estate had housekeepers who likely used their own vacuums for cleaning, leaving the owner's vacuum in the closet.