Hmmm, they're pretty different bags.
If I had to judge based on the current information given, then I would choose neither.
I've never had either bag so I can't comment on wear and tear. The only thing I know is that people apparently have lots of issues with the Boy bag and the lambskin that Dior uses tend to be on the delicate size.
I can't wear metallics well, and I prefer the D-joy in a medium size (or at least a small).
If the D-joy you were looking at was a small or medium, I'd definitely go for it though.