I own & like both, but I honestly kind of prefer the drydown of Individuel more. My favorite part of both fragrances is the juniper berry/herbal type strong top notes. And Individuel seems to hold onto a bit more of that sharpness in the drydown, while Original Santal's tonka and vanilla create more of a "lipstick" type accord when they mix with the other notes in the drydown.
It kinda depends on which phase of the scent is your favorite. If you like the sharper top, then I'd pick Individuel, but if you like the smoother, powdery sweet drydown, then I'd go with Original Santal.