Well, for start the two trackers are work a bit different.
The features Madtracker has that Renoise don’t are Rewire as you allready said, keep samples on disc and its easier to create multi sample instruments. Madtracker also have better support for xm/it.
Anyway I know both trackers very well and I prefere to work in Renoise. Because I currently tip towards the features Renoise have that madtracker has not, more than the features madtracker have that Renoise does not.
Its probably more a matter of taste…
Anyway madtracker is also a nice tracker.