I think you would have to ride several "across the spectrum" to make a comparison. I do not have much experience w TB's. But, QH's are all over the map...some of the larger "pleasure" builds have a different "feel" than the smaller, "stockier" cow horse types. And, just like any individual horse...you can get them in that "perfectly smooth" motion, or one that is unchecked and uncomfy..to say the least.
Within our Paint herd, I compare our two wide bodied, halter bred mares (mother/daughter) to locomotives. When you're riding full speed, those big muscled hind legs are churning and pounding the ground with drive. You can just feel the power. Our long backed, penning mare has a very smooth, long stride that just eats up the distance with no effort at all, and our leanest, short backed mare feels like she is floating along over the ground.