I think that SIMATIC IT is a suite of software that Siemens sells as an MES investment for companies. I'm sure I read somewhere that the core of it originated in an Italian company they bought some years ago. Orsi Group? The Historian component or module is presumably part of this suite.
As to which one is best, WinCC or Simatic IT, you could also ask which one is best, a saw or a hammer? What do you need it to do?