The type of platform you should choose depends on the software you plan to use to power your website.
Generally, you should choose Windows if your website is built in ASP, ASP.NET or requires an Microsoft SQL database.
If your website is built in PHP, Perl, Ruby, or Python then choose Linux. WordPress, Joomla!, Drupal and all other Web apps we provide through our one click installers are optimised for our Linux hosting platform.
If you're only using WordPress, then we recommend using our WordPress hosting platform (it has WordPress-specific speed-boosting features).
If you're still unsure, we'd recommend choosing Linux as this platform meets the majority of our customers' needs.
If you need further help choosing which of 20i's hosting packages would be right for you, please see: How to choose your web hosting.