I just wanted to write that after 48 hours it seems Tiffany won! Very telling as I even posted on the Cartier sub!
Thank you very much for your opinions and advice.

Thank you very much for your opinions and advice.
Thank you... Cartier is definitely the most classic of all and you're right - its so understated.The Cartier set would be my choice for you. It's classic, elegant and understated, and looks beautiful on your hand.
I agree that Cartier looks the best on the hand it looks like its already mine?!Cartier, it works on your hand like a dream, even the stone looks a better colour
Thank you so much for your kind words. I guess in hindsight there's a reason why I posted this on the Cartier forum!I have no allegiance to either brand, but imo, the Cartier ring blows the Tiffany out of the water. The
lower setting of the diamond, and the way it looks on your hand - Cartier 100%!
Good luck with your decision, and huge congratulations on your upcoming engagement!

Wow, this is why I love purseforum, such an amazing tip! Thank you @emo4488 you saved me from heartbreakTiffany! I'm biased b/c I have a similar 6 prong. Although at the time I really liked the look of the 4 prong. Our jeweler insisted 6 prong will be more protected from loss.
I do advise against the Tiffany band you tried. The exposed diamonds will chew up the prongs on the setting. It will still be fine just cosmetic and create a groove on the side of the prongs. It's like the diamond saws into the metal. You might want to consider a setting where metal touches metal vs. metal to diamond.
What did you end up with in the end? Curious as to how you came with your decision! Its supposed to be a ring I am to wear every day forever until I die... I have trouble making such a big decisions.My vote goes to the Cartier 1895, as I was leaning heavily towards it when I was ring shopping. Classic!
Thank you @casiecn I agree Tiffany is the round, feminine look! The way the setting is so high is like a crown on top of a hill.Congrats on your upcoming engagement! I prefer the Tiffany on you in the photos. It looks like it fits your finger/hand better since it is more soft on the edges (rounder looking due to prongs), more elegant looking. The Tiffany diamond sparkles more in this setting based on the pictures.
Thank you for the vote.. You're right.. I can't go wrong with either choice.I think both look great! I would go with which one feels more comfortable. I voted Cartier because I like lower settings but that’s really personal preference. They both are good choices!
Thank you @Pop Art Suzy the Tiffany setting is sooo iconic. Even my fiance-to-be prefers the Tiffany.....!I voted for the Tiffany setting. I just think it sits better on your finger and sparkles so much more. I love the 6 prong and how it looks on you. I think it's just stunning. Congratulations on your upcoming engagement.
Thank you @A bottle of Red !!!! Same vote as my partner!I love the six prong so I vote Tiffany