It all depends on what you want to do and how "easy" easy to use is. I tried Amapi 4.whatever and it was all right. I don't like the interface and I was thoroughly unimpressed with the mess it would make of complex booleans. But, you can get Amapi free if you know where to look. (Sorry I can't direct you). I've since switched to Rhino. It might not be the easiest to pick up, but it only took me a week of constant tinkering to get fantastic results. The best thing about Rhino is that it can do just about anything I can dream of. Heck, there are lightwave and Maya users that would rather model in Rhino. If you are looking to make some vairly complex shapes but are willing to leave much of the detail in the texture then a cheaper modelling program will likely suit. Like I said, it really depends on what you intend to use it for. Just my $.02