Both vehicles are made for different purposes so it really depends on what your lifestyle is. By the way, there are threads for both vehicles here, for the Dmax you can go to the Dmax owners thread under diesels, suvs category then there's a Hyundai Tuscon thread in the car comparison forum category.
What I can tell you is that (as a Dmax owner) when you say "Isuzu diesels are kinda smoky" then I think that you are referring to the old technology diesel engines. The Dmax's 4JH1-TC Intercooled Turbo Charged Diesel burns cleaner emissions compared to yesteryear's engines. Perhaps if you research even more in the numerous threads regarding common rail direct diesels, you might be surprised that newer does not necessarily mean better

.
The Tucson has been turning up good reviews inside out either from actual owners or auto reviewers. For me, the Hyundai brand is a force to reckon with in today's auto industry; ride or drive the ever popular Starex and you'll understand why it is more favored than it's korean cousin Kia Motors.
But the best advice I can really give you is to Test Drive BOTH cars to feel for yourself

. Until today I'm amazed by the number of car buyers who invest in a ride that they have never even driven!
Good Luck!