If you only need the general "type" of os (ie, Windows, Mac OSX, Linux), I've found the best solution is to use os.name first, as it's result is guaranteed to be one of only a few values, and then platform.system() to get finer grained results (ie, differentiate between OSX and *nix).
The problem with just using platform.system() is that it's return value isn't "guaranteed" be one of a few values, as the Python community learned when Vista was released. Whereas previous versions of Windows would return "Windows", Vista returns "Microsoft". While this may be considered a bug, it taught me that it's probably safest to just use os.name when possible, and only resort to other methods when this doesn't provide enough information.
Unfortunately, this is the case when trying to differentiate OSX and Unix/Linux - os.name returns
'posix'
for both. So there, we resort to platform.system(), which will return 'Darwin' or 'Linux'.Of course, you may need more fine-grained information, and there's other functions that can help with that - platform.uname(), platform.system_alias(), platform.uname(), maya.cmds.about() if Maya is initialized, etc.