The question is what do your really want. If you are serious about your dressage you want to make sure the resulting cross has the physical build and movement to be successful in dressage. Starting with a TB mare your resulting cross is already 50 percent TB, which assuming they are quality mares, should give you enough gallop and endurance for cross country. I’d look for a stallion that will add a bit more uphill and some more elasticity and scope to the gaits to improve your dressage.
Othere things to consider are rideability, how good a rider are you? What type of ride do your like?. What is the disposition of your mare? Do you like a hotter more reactive horse, or are you more comfortable on a more ralaxed type of horse.
I quite like these two fairly new stallions on TB mares as potential Event/Dressage producers.
Fabregas (Florencio/De Niro) Recent import
Panoramix Amaire (Concorde/Formateur) older guy, recently approved, retired show jumper.
They are very diffrent type horses…it really depends on what your mares are like, and what you prefer.