Okay, since everyone is talking C4D in here, I will share my opinion as well. I have been watching C4D evolve for quite sometime. It caught my eye several years back, when it was C4D 5. But those where the days when searching with C4D as a keyword would barely return any results. It has come a long way since then. Now there is 3DFluff, 3D Attack, Vital Exposure, and CmiVFX and of course, Cineversity itself and also C4DCafe tutorials by 3D Kiwi and C4DPortal tutorials by Mike Bachelor. But the basic problem with C4D is, nothin in C4D works like any other standard 3D package out there. You know NURBs modeling in XSI, you can do NURBs modeling in Maya. Even the keywords will match, e.g. CVs. But then, if you fire up C4D, you will suddenly get stalled. Nothing works here like it was used to be.
Everyone here praised 3D Fluff a lot. But the biggest pitfall of 3D Fluff is, they always seem to dodge any complicated modeling part. What will you render, my brothers, if you can't make the thing you want to make? Regular shapes like a bicycle or a car tire or a trendy Porsche's outer body are not difficult to make with C4D. But if you try to model a sailboat or a Chevrolet Bel Air, you will understand life is getting difficult for you! Well, of course, the veterans won't agree with me, and they don't have any reason to. But, C4D has no extensive modeling tutorial/literature. Everyone seems to bother about rigging, texturing, lighting. Some apparently not related tools, like Google SketchUp, can be used to make some infrastructure, which can be ported to C4D, but capability of such softwares are very limited. And of course, ready framworks made of long single isoperms are not always good to begin with, if you are a fan of surfacing and lofting.
If you don't know anything at all about any 3D package, XSI is something you should never try, because you may feel so confused in the control jungle, the word 3D maynot bring a happy memory to you ever again

C4D miraculously clicks for some. They should stick to it. For anyone else, with a heavy duty machine, Maya is the "safe" choice. Progress will be slower with Maya. Rendering will be more burdensome. The software itself will look so yesterday ( C4D looks genuinely sexy as does Modo ). But chances are really low, if at all, that you will sit idly thinking "Only if they had made some quality tutorials on this area, perhaps I could get some work done by now".
Now, that all being said, C4D is actually a very good choice :) I am still trying to learn it when I am getting bored of Maya, but sad to say, all that I made so far that made any sense were all in Maya and none in C4D. But I always try to promote and love to talk about C4D, not Maya
I hope my post is not been too boring to read!