I don't do 3D art, but I do do 3D modelling and design frequently (I guess those could be considered art depending on how you look at it ) , so I'll provide some input on some programs I've used. Google Sketchup is a really good free 3D modeling program also, I've used it a few times. It's easy to use (VERY small learning curve) and can make some really nice looking models. AutoCAD is also really good if you have access to it, but you need a really amazing computer to do in-depth 3D modelling with it, and it has a very steep learning curve. I haven't checked out the ones you posted but I'll have to see what they're like!