Well, I'm extremely caught in a hard place with this question. I initially came to serebii forums to be a spriter way back in the day(gen 3 actually), so I definitely have an affinity for it. But at the same time, I am now a 3D modeler/animator, and rarely do any spriting.
I have to go with the models personally though. Having made my own pokemon models, I have kind of my own personal appreciation for how exceptionally well crafted each and every one of them are. You can definitely tell Gamefreak wanted to wait until technology reached this point, so they never have to remodel any of the current pokemon again, every single one of these models can be reused for future games with no issues.
Also for those saying the pokemon's colors are "dull", well, they aren't. I've looked at their textures and they are true 1:1 matches with their sprite counterparts. The issue is that unlike sprites, they have light cast on them and that makes them appear duller then they really are. Either way I think they did a perfect job on them.