It depends on what you're using the site for. If you're wondering about straight SEO results for .net or .com, there likely won't be a difference as they're both main TLDs. If the site is used for mainly one time visitors or is strictly online, you should be fine with a .net. If people are mainly getting to your site by searching or possibly bookmarking your site, it won't matter between the two.

On the other hand if you have an offline business, I would definitely go with a .com. 9 times out of 10 if you give someone a business card with MyCoolDomain.net, they will type in MyCoolDomain.com. It's just habit. Try it with friends and tell them to go to YourSite.net while standing over their shoulder. I bet even then you get most people going to YourSite.com. If it's off-line, you want people to remember the main domain and not have to worry whether the TLD is .com or .net. They just automatically guess as .com.