Actually, if he likes building in level editors, I don't think the issue is as much the package as well the learning material. Find the best mesh modeling tutorials you can find, and then get him that package while he follows the tutorial. That way he can get up to speed on the boring technical stuff by following a good…
my recommendation for the kid which loves Minecraft; Sculptris for ease of usage and to quickly get into 3D sculpting + Blender since it has Dynamic-topology sculptingin it which makes sculpting even easier and all the other nice things you could wish to use in a 3D Program like gpu rendering to have quick results which a…
3D studio max seems the easiest to learn and most forgiving. It's less complex than Maya (no history, no complex node management) and more intuitive. Especially for modeling the modifier-based workflow is pretty well suited for a beginner and for a clear and logical step by step approach. I actually started and taught…