I know you said don't go by ring style but for me ring style influences ring placement.
I have small hands with short fingers (I know it doesn't appear so in photos but that's because my nails give the illusion of length).
Therefore, for a relatively bigger/bulkier/thicker ring, I would prefer it on my middle finger which is the longest and therefore would look the most balanced compared to my other fingers.
Looking at your photos I think that honestly both look great and could work either way.
But if I had to choose, based on the size of the diamonds (I know they're not the exact same ring but are close enough to me), I'd prefer it on the middle finger.
A couple of things to consider:
1) Are you a ring wearing person? Do you like to wear multiple rings? If so, a ring on your middle finger would potentially limit the rings you can wear on the fingers next to it, especially if you're concerned about scratches and comfort.
(I am a ring lover so I do like to wear multiple rings and sometimes I will put rings on my pointer and ring fingers to be able to wear more. Wearing rings right next to each other are usually uncomfortable and will scratch each other.)
2) Generally speaking (though it can depend on the design of the ring) wearing rings on the middle finger are more comfortable and user friendly. It's also based on your comfort level and everyday tasks that you do with your hands on a daily basis.
Just my 2 cents but hope it was helpful! Good luck and happy shopping!