the main difference i see is that with the tube  it is necessary to have bulk to feed  the operation .... once the material in the tube reaches the same weight as the material out of the tube  the operation is no longer effective .....  with the screw ...  the material is being sucked in  and will continue to work as long as any material is fed into the intake .....  so ...  it all depends on what you are doing ... the sand that is recycled over and over again  is a good example of the tube being right for that job ...... in a grain silo ...  the necessity for all the material to be taken in  would be a good example for the screw