major Operating System manufacturer uses .org as their domain suffix. Microsoft.com, Apple.com, Redhat.com. Given .ORG should be considered
ROS is not a manufacturer, not a company, actually ROS community is a part of ReactOS source code and must be located at sourceforge. Will they register "dot sf" as a first level domain?
Have them both point to the same place. You don't gain anything having a .org or a .com extension. The important thing is they find the website. Of course you could always have it set up as a backup. When Reactos.comhttp://Reactos.comgets slashdotted, the people who know about it could get to ReactOS.org (assuming they are on different web servers).
My 5 sentences.