This depend on what exactly you are trying to do with the VPS. For instance:
1. If you simply want to use it for email purposes - either of the two platfroms will do. Both VPS platforms supports email services (POP3, IMAP, SMTP) and webmail.
2. If you will be using it for website hosting:
Choose "Linux" if you will need Apache web server, PHP and MySQL databases. Although PHP and MySQL also works on Windows but its performance is better on Linux environment. Also, if you will be using CMS such as Joomla, Wordpress or Drupal, it's ideal to use Linux.
3. If you will be using Microsoft technologies such as ASP and ASP.NET, you should select "Windows" VPS.
If you are still not sure and your requirement does not fall on the details above, kindly contact our Sales team for assistance.