I think there are several apps that do basically the same things, with a few unique twists, and different GUIs. Most of them can use the same renderers, there are shader overlaps, tool overlaps, etc.
I've seen many many debates over which is best. It always seems to come down to user preference.
For hobby usage, pick what you like; but, some professions tend to use one app over another, and that is what determines which is going to be used. XSI could be a thousand times better than MAX; but if you are working for a arch-viz company that uses MAX w/ VRAY; you are going to use MAX w/ VRay, 40+ hours a week. If you are a FX guy in a studio using Maya, you will use Maya. And so on.

Competition is good! Gets the software corps. off their asses and into R&D. If there was only one app. in the world; it would never get upgraded.

Friends don't let friends use booleans.