While I do agree with Dan in terms of there being no difference except for human perception you should not underestimate perception or behavior, the majority of ordinary web users will often default to typing .com (as it is the most percieved to be common extension if they do not know or remember the complete website address) therefore if the .com is available it may be a good choice to go with.
even though there is no difference in .com, .net and .org in terms of how google ranks them, people’s recognition and preference towards .com sites will generate much more traffic and attention which will yield better results for your adsense!
While that is a very good point, there is a large trend of people typing URL’s directly into search engines rather than the address bar (especially if they have google et al as their homepage) which is affective in both direct and indirect traffic. I guess Google got to that stage where people genuinely believed it was the Internet.
I think taking the com and net is the best thing, they are both not that expensive and you don’t run the risk that someone else gets the Domain and offers similar services under the same name only with net