I own this and I have to admit that, even if I find the game slightly overrated, the cards are well made and above all I find the quality of Ghenos Games components very good.
I agree that the cards are great! Have you heard of the Fan Art Pack? It has variants of a bunch of the cards in a different style, which I also quite like.
My favourite cards artwork is also my favourite board game, Oceans ( https://www.northstargames.com/products/oceans ) ! Especially on the collector edition with holographic special cards, really cool artworks overall (and really good game too)
Arkham Horror: Beautiful illustration, as well as a beautiful game in my opinion.
MtG: Magic cards remain among the most polished and beautiful ever created, even if I hate the direction it has taken, and in general I appreciate competitive games less and less in favor of more collaborative ones; in fact my favorite way to play Magic is with the Archenemy format (there is also an excellent boxed product).
Marvel Champions: I don't actually have this in my collection but it looks pretty cool, I have to admit I'm quite a fan of Fantasy Flight Games at the moment!
50% of MtG products are now "Beyond Universe" cards, third-party intellectual propriety such as SpongeBob, Stranger Things, Doctor Who and more; and they are all standard legal.
Here a video if you want more details: https://youtu.be/7us923DG-Gg
I don't know about most beautiful but Dale of Merchants and Ascension have some of my favorite card art. I also like Mottainai for it's aesthetic simplicity.