I don't believe this has been discussed here. There's lots of criteria, more than would meet the eye I think. I was thinking about this and there really is so much subjectivity to it and how not one person will agree on the same exact idiosyncrasies. If you were to make your own playing card from scratch and be able to take different characteristics from all of the cards out there, what would you like to make? To make it easy, this can be broken down into categories as below, and feel free to add your own too! I'm curious to see what everyone thinks.
Card Size: Bridge or Jumbo
Card Material: Paper, Plastic PVC, Plastic Cellulose Acetate
Pip Index: Standard or Jumbo
Card Back Color: Red/Blue, Yellow/Black, Green/Orange, Purple/Green. Green/Brown, Green/Yellow, other
Card Ink: Red/Black or Four Color
Card Red Ink: Casino (darker) red or cherry red
Cream colored center on aces and number cards: Yes or No
Card Face Font (this one can get very subjective): Kem, Bicycle, Copag, Gemaco, King Australia, Cartamundi USA, Cartamundi Belgium, Fournier, Piatnik, Dal Negro, Modiano, desjgn, Zero, Faded Spade or write in your own
Card Stock Thickness: Thin, Thick, or in the middle
Card Back Stock: Glossy, Smooth, Matte, Linen, Coarse, Textured
Card Face Stock: Glossy, Smooth, Eggshell (akin to King Australia) Matte, Linen, Coarse, Textured
Card Back Design: This one is too subjective and there are too many out there. Write one in.
Below are my ideal card characteristics. Feel free to post photos that show each characteristic where applicable as I will below!
Card Size: I actually can't decide on this. Poker for NLHE only events, Bridge for playing any other game with more than two hole cards
Card Material: I'll have to go with Plastic PVC here. It will be difficult to go with cellulose acetate for a couple of my other descriptors below, will get to that. That, and the cellulose acetate decks that I own, although they feel really nice out of the box, have an approximate 25-30% warping or bowing rate after checking on them months later after getting them into play. I'll have to go with PVC for the durability factor. Knock on wood, I haven't had a PVC card chip or break on me yet.
Pip Index: Jumbo
Card Back Color: Can't beat the classic red/blue, but I'll throw an interesting one out there....orange/black or pink/black
Card Ink: Red/black
Card Red Ink: Casino red

Cream color card centers: Yes
Card Face Font: Cartamundi Belgium. It's the nuts to me, thought I know some aren't fans.
Card Stock Thickness: Somewhere in the middle, but if push comes to shove, I like a thicker stock rather than thinner.
Card Back Stock: Textured back a la Dal Negro Virgolone and desjgn Grand Victorian
View media item 19035
Card Front Stock: Give me the eggshell soft as a baby's bottom card stock of the King Australia cards here.
Card Back Design: Give me the desjgn Grand Victorian artwork here

Card Size: Bridge or Jumbo
Card Material: Paper, Plastic PVC, Plastic Cellulose Acetate
Pip Index: Standard or Jumbo
Card Back Color: Red/Blue, Yellow/Black, Green/Orange, Purple/Green. Green/Brown, Green/Yellow, other
Card Ink: Red/Black or Four Color
Card Red Ink: Casino (darker) red or cherry red
Cream colored center on aces and number cards: Yes or No
Card Face Font (this one can get very subjective): Kem, Bicycle, Copag, Gemaco, King Australia, Cartamundi USA, Cartamundi Belgium, Fournier, Piatnik, Dal Negro, Modiano, desjgn, Zero, Faded Spade or write in your own
Card Stock Thickness: Thin, Thick, or in the middle
Card Back Stock: Glossy, Smooth, Matte, Linen, Coarse, Textured
Card Face Stock: Glossy, Smooth, Eggshell (akin to King Australia) Matte, Linen, Coarse, Textured
Card Back Design: This one is too subjective and there are too many out there. Write one in.
Below are my ideal card characteristics. Feel free to post photos that show each characteristic where applicable as I will below!
Card Size: I actually can't decide on this. Poker for NLHE only events, Bridge for playing any other game with more than two hole cards
Card Material: I'll have to go with Plastic PVC here. It will be difficult to go with cellulose acetate for a couple of my other descriptors below, will get to that. That, and the cellulose acetate decks that I own, although they feel really nice out of the box, have an approximate 25-30% warping or bowing rate after checking on them months later after getting them into play. I'll have to go with PVC for the durability factor. Knock on wood, I haven't had a PVC card chip or break on me yet.
Pip Index: Jumbo
Card Back Color: Can't beat the classic red/blue, but I'll throw an interesting one out there....orange/black or pink/black
Card Ink: Red/black
Card Red Ink: Casino red

Cream color card centers: Yes
Card Face Font: Cartamundi Belgium. It's the nuts to me, thought I know some aren't fans.
Card Stock Thickness: Somewhere in the middle, but if push comes to shove, I like a thicker stock rather than thinner.
Card Back Stock: Textured back a la Dal Negro Virgolone and desjgn Grand Victorian
View media item 19035
Card Front Stock: Give me the eggshell soft as a baby's bottom card stock of the King Australia cards here.
Card Back Design: Give me the desjgn Grand Victorian artwork here