This really depends on your brand and how big you thnk your website will be. .net or .org doesnt matter as long as the quality of the content is good. However you dont want to use the .org then wake up one day and find a new competitor using the .com and taking away business and traffic from you and then after that yet another competitor starts using the .net why its best to buy all 3 extensions! You dont have to actually use all 3!! My advise, find a simiar .com then also buy the .net and .org and just park or redirect those other two to your .com site. You now have set a barrier to others using that exact domain name. If you must have that domain name then buy both .net and .org and redirect one to the other. If you get a different .com then also buy the .net and .org and redirect the domains. Up to you really but no difference in .net or .org really and nothing to do with networks or charities as one or two mentioned who have no clue.