Theres also 3DS Max and Maya, both of which cost a few thousand dollars, and Blender, which is free.
Milkshape is good for beginners starting out with modelling, but you can't do anything other than making models for games, hell, I don't even think it can render the models. I won't talk about 3DS and Maya's features, as I don't know them, and I doubt you can afford them, but Blender can do stuff like physics simulations, water simulations, and a lot of other stuff.
Not to mention flat shading in Milkshape is a pain in the ass, while it's already done for you in Blender.
Go ahead with the 30 day Milkshape trial if you want, but I'd recommend at least trying out Blender and learning some stuff with it before buying Milkshape. There are some tutorials on the web, you can search google, youtube, or check out the ones on the Blender site (
www.blender.org)
