I agree the craftsmanship should be equally excellent in both. I would choose based on style.I have both and think they are pretty much equal in quality. The only difference I've seen so far is I find the Dior lamb to be more durable than the Chanel lamb.
You didn't mention resale but Chanel holds its value better than Dior.
Between the two, I would decide based on the style. I don't think you will have any quality issues with either one.