I have taken local Thai busses as well, and they don't compare to the VIP busses that most tourists seem to be taken. I recently took a bus from Udon through Sakhon Nakhon to Nakhon Phanom, and it took over 5 hours, very impressive considering the distance.

Of course even the most dodgy Thai bus can't compare to the regular Lao busses They stop even more and seem to be driving slower.