I like my 650b x 38 tires and they are more stable, especially on our crappy roads in NE. I understand there are still smooth roads in other parts of the country, but in MA such a thing is an abstract concept.
On the other hand, a bike with a lot of geometric trail as well as pneumatic trail might be too stable for some situations. That is the rider might not be able to manuver quickly enough to avoid a hazard in the road.