I don't model that often, but when I do I turn to Rhino as my app of choice. I just like the way it works and, when I am modelling a lot, I find I start analysing real-world objects in terms of how Rhino would realise them.

I also have Lightwave (6) but as yet I haven't had enough time with it to get beyond a few of the basic tutorials. Maybe that's why I haven't upgraded yet...