I agree with Dubdisciple. Sonar is a linear sequencer. FL Studio is a more like a tracker. The Step Sequencer is a sort of tracker superimposed on a linear sequencer. FL s has gone through a lot of changes since first got version 4. I am now on version 10. Underneath it all is its tracker soul.
FL is ideal for certain kinds of music. it can be used to make any kind but it excels at creating dance and trance type music. Where Sonar is a general purpose DAW that can do any sort of music but excels at none. It sort of does all sorts with more or less the same ease.
For me its logical and works the way I think. FL is not as easy for me but I can use it.
I don't have any real experience with Reason and can't comment on it.
I do know that Sonar, Cubase and Logic share the same underlying philosophy. They all came from first being sequencers for MIDI.
As to the ease of use, these program cut there teeth on MIDI controllers. FL did not. Thus on the surface it seems that FL is better for mouse users and that to a degree is true. But there is nothing like hooking up a good controller and jamming away on Sonar.