Not that you really get a choice. You buy the hardware and get the software platform that comes with it. You cannot put Win8 on RT devices and you cannot put RT on Win8 devices. I see that Flash installed on RT will only run on sites approved by Microsoft.
RT comes with a full version home/student edition of Office 2013 installed. H/s does not include Outlook. If you were going to buy h/s for only one device then the h/s saving might sway it towards RT.