What do you mean by tubular track? All coaster track styles (except Itamin S:TE style) have tubes...Do you mean the Vekoma/Arrow tracks style? Because even those can be smooth. Booster Bike, Velocity, Tennessee Tornado..etc
I find that smoothness is not determined by the track, but rather how the designers shape the track and by car design. Example - Old vokema, cars have large gaps on the wheels which make it rather rough. Togo has possibly the worst transitions making that not smooth, you get the idea. If they designed them all in a certain way, and thier cars a certain way, any one of those tracks could be just as smooth as the other.