I would say this depends on your programming experience, if your used to C like syntax and think that way, i.e curly brackets, semicolons, strong typing, go with the C++, its fast, and its the language you know.
However if you comfortable with programming languages as a whole, then python is not a bad alternative, and I would highly recommend the panda3d 3d engine (I consider this more of a 3D engine, rather then a game engine in the sense you still have to build game specific logic), it uses python and I think the newest python 2.6.xx version is your best bet. As far as performance, unless your running an older machine, interpreted languages such as python can run nearly as fast a compiled languages such as c/c++.
