Hi Daniel,
My favorites tend to be the cards which most strongly embrace the aesthetic of their era, and I like cards with bold, striking designs in general.
I agree with kq76's comment about the 50's cards, and in my opinion this extends to the 60's cards as well. To me, these cards are more muted than these turbulent, lively decades warrant, and in general I'm not so fond of the out of focus ballpark backgrounds. I attached some examples of IRL cards from the era which I quite like - simplistic but colorful and rich in contrast.
For the 80's and 90's cards, I would enjoy seeing more 'extreme' designs. There were so many garish cards back then (see attached), and I wouldn't mind if you leaned into that some more. I like the triangular 80's HW Heroes / Historical Legend logo and the 90's neon HW Heroes one as well.
I also agree with Splitter24: more variety and 'go nuts'
One last idea: would it be possible to have multiple versions of the 'banner' which contains the player's overall rating? I like the current design, but it seems to suit modern cards better than some of the older ones i.m.o.
Thanks for the work on the cards so far, I look forward to seeing more of it!