I use Hexagon 2.
It's not a bad tool, in fact it's pretty well featured. Prior to 2.5 update I used to find it buggy, mind you since 2.5 I've not done a lot of 3D modelling, so I've not been able to stress it.
It is designed exclusively for speeding up modelling and it comes with a decent set of tools to do that.
Some cool features that make this worth grabbing before the offer runs out:
It comes with a fairly decent UV Mapper. I didn't used to use it because it was buggy...but this was version 2.1
It comes with tools to directly paint your texture on your model in real time. Of course, you'll need to UV Map your model first. It also can use texture brushes, which is pretty handy
You can go into extremely high detail (like ZBrush users can) with its displacement brush. I made a few models doing this, but at a time when I was crap at it XD.
Bryce is probably a good solution for creating Sky Boxes, I never really properly used it, so I am unsure of what features it can use.
Daz Studio (dunno if Pro is any different), but last time I checked you couldn't rig your own models in there, it seemed more like Daz's own take on Poser, where you're able to use customise pre-made media and create scenes and animations. It might be fantastic for visualising a rendered scene before you've modelled it.
Also, all of their software is available for PC & Mac. You get a total of 4 download tries. If you purchase the software it's 10 (for each version, so 10 for PC download and 10 for Mac download.
Downloading Hexagon again, might come up with something to demonstrate some of its features for those interested.