Upload & Sell: Off
I had a very good 28 F/1.8, good wide open, very sharp at F/2. I had this as a set of 3 F/1.8 lenses for low light shooting (28 F/1.8, 50 F/1.8 Mk I, 85 F/1.8).
I upgraded these all to Ls, because one never has enough light when shooting low light scenes . Since there is no 28L, I got the 24L Mk I to replace it, and was very worried, because of comments on the internet at the time, despite it being tested as a world class lens in its category.
I sold the 28 F/1.8 a few months later, even if a little reluctantly. That says it all.
When the 24L II arrived on the scene, I wasn't going to get one, I was very happy with the Mk I. This only changed when someone offered me new price for my Mk I, so I used that as a down payment for the II.
Differences, yes. Big ones? Not that much. A little sharper in the corners, less field curvature, less CA, although I never really noticed any with the Mk I anyway. All stuff you really only see in very large prints from close up. The main difference, I find, is that the Mk II is slightly better at focusing.
Othe rthan that, both have great rendering, and amazingly good bokeh for a WA.
In short, the 28 is good, but the 24 Mk I is better, and the Mk II slightly better again.
Kind regards, Wim