Thomas, may I ask what 3D software you are now using, or are you still using Softimage, just without any support or maintenance?
Several, I'm still in a testing and evaluation phase.
For rendering, I honestly like Lightwave a lot and rendercost is unbeatable. Many other things in the app feel rather ancient, but the renderer is just as good and flexible as ever, if not better.
I also have Fprime - still amazing.
MoI is my translator and go to software for everything NURBS - with XSI in the pipe or not. ;-)
For rendering I also own Fryrender (not recommended because of a stupid company behind it), Octane and my current favorite for photo-real: Thea render - http://www.thearender.com
Then I'm heavily testing and learning Blender. There are so many brilliant projects going on with it since the 2.5 overhaul, it's breathtaking - 2.6 is just about to be released with some of the Summer of code projects in it.
I like a lot of what I see but there are also a lot of limitations, compared with XSI.
I guess in one or two years this could become my software of choice, maybe combined with Vray, since a real production renderer is what's missing most IMO - and that works already very well:
For visualization, a friend of mine is using Cinema 4D and jobs we do together may be done with that, for data transfer simplicity - It's definitely not my personal choice but it works and it's easy to use, if pretty bland - I actually started out with it before I switched to using mostly Lightwave back in the days...
And sure I'll keep XSI around. It's the software I'm the most fluid in ATM and ICE is pretty handy.
And no, an Autodesk software is not on the list of alternatives ;-)