Should i install SP 2013 or 2010 if i want to start a new SP 2013 project

Dear Sirs,

I want to start a new SharePoint 2013 project, so I want to know which approach I should follow:-

1. Should I install SharePoint version 2010 Or 2013 which is on its RTM stage.
2. If I install version 2013 RTM, can I easily upgrade it to the public version which should be available soon (as I have read) after the current RTM version. Or it is better to install SP 2010 and upgrade it to 2013 public version ?.