Remy Martin is offocially branded a FCC (Fine Champagne Cognac) which means it
is made with very specific types of grapes at specific rates (I believe it is
51% made from Grande Champagne grapes, and the rest from Petite Champagne
grapes), whereas Hennessy is not.
This does not refer to a drinks' quality, much to many cognac houses' dismay,
but to the details of its making. Very few people are capable of discovering
the different nuances in eau de vie by its grape-type, I believe.
Also to be noted, Remy Martin does not have a VS level. They have a VS Grand
Cru which is a relatively newer brand, but Im not sure it can be compared to
Hennessy VS as they are not in the same category.
Frankly I would prefer neither, but of the choice, Hennessy would be mine.