Depends, if you are selling something I wouldn't use .org. IMHO .org is for organizations and info sites not ecommerce. They all hold equal weight for SEO.
I would say .org, but as was mentioned above, .org is more for sites that are non-profit organizations, at least that is how it was originally intended to be.
.Org, but it has to be a charity/info site, otherwise i believe The "domain people" have the right to take the domain away.
Depending on the name/site in question. I believe that dotUS is becoming more and more relevant for US based companies to showcase their goods/services especially where a dotCOM is unavailable or unattainable for that business. Although I do agree with others that dotORG currently is favored by Google and Yahoo, but this will change in time.
.org is good in Google, but Yahoo! considers .US higher. But since now Yahoo! are using Bing. I still dont know how it will be going. However, I think .org is good.
org is much more popular than the other one , so i guess since there isn't much difference so i will just go on with the more popular one
It depends on the domain. Personally, I like .us over .org, but it really depends on what is in front of it
.org is really meant for non profit related websites so if u cant get a .com and ur site has nothing to do with charities or non profits then maybe go for a .net or try harder to find a suitable.com.