Both are great and interesting fields. You can't just compare one with the other and it completely depends on your interest which one would you deem fit for yourself. These days digital marketing is everywhere and ample amount of opportunities are available but for luxury brands it's not present everywhere. So if you want a career which will land you a job easily then go for digital marketing 

One of the esteemed professors who teaches Executive MBA classes & luxury management electives ( certification course as well ) in one of the biggest business schools in Europe once told me, Luxury is not about needing something or seeking comfortit is about WANTING,the need to posess.

So, if you are up for the challenge go for luxury management. Marketing is established worldwide and is a sure shot but if you like an adventure and would deal with one of the growing markets then Luxury management it is.