EF 70-300mm f/4-5.6 IS II USM vs 70-300 IS USM V1 vs Tamron 70-300 SP

I am looking for one of these zooms. I have a chance to get the old one used at half price of new, so that is a factor.

I read a review of the version 2 and they suggested the V1 might be a little better optically. Is that true? I know the V2 focusses faster.

Am I going to lose much in picture quality if I stick with the version 1 of this lens? I am using it on a 90D camera. Anyone else do this comparison? I want to stick with a full frame lens, so I can use it on my film cameras too. And possibly mirrorless cameras down the road too.

My other option is the Tamron 70-300 SP lens. What say you?

"Opticallimits" thinks that the Mk II Canon lens is better than the Mk I, especially at the longer focal length (where most consumer grade lenses tend to show reduced sharpness). Since it focuses faster and will remain repairable (by Canon) longer, I would go with the Mk II unless cost is the deciding factor.

Canon EF 70-300mm f/4-5.6 USM IS II - Review / Test Report