About the different step handlers

Hello everybody.
I have looked into the wiki, I've searched into this forum, for ode web, for google... But I haven't found anywhere where the different types of OgreODE step handlers were explained. I think that the list of OgreODE step handlers is the following [I'm based in GranTurismOgre example]:

1. 
   StepHandler
   ExactVariableStepHandler
   ForwardFixedStepHandler
   ForwardFixedInterpolatedStepHandler
   [/list:u]
   
   Like the example, I also need to control a car. I would like to know what is the most suitable for my application.
   
   Thanks.

As far as I experienced they represent the different ways to handle time differences in the scene. So the differences only would be obvious when varying the time per frame.