Autodesk 3ds max is what I use. plus you can get it for free. Maya as far as I have heard is supposed to be better, but I think it only better in that it has more support for animation. Zbrush is amazing but requires monies and a touch pad stylist thingy. Mudbox is the poor mans zbrush. zbrush, mudbox is generally for soft modeling. maya 3ds max is more used for hard models. Idk bout memory but 3ds max is only a gig and a half. Photoshop is also nice to have for textures.