I think it looks even more stunning in person! I think the Diorama makes more of a style statement than the Marmont, and I think velvet bags won't wear very well (since velvet is delicate). I also like the colour and think it would go well with a lot of other colours.
Pros for the Marmont - you could probably fit a bit more inside it than the Diorama. It's also a beautiful colour. More "on trend" style, if that's something you like.
For me, this would be an easy decision, because the Diorama makes my heart sing. But you don't seem taken with it? Why did you buy it in the first place, and why are you not sure now?
Bottom line, it's not worth spending that much money on a piece you don't love, imo.