Generally speaking, you will always want to go with a .com domain name. .Com is by far the most common extension. Most people’s first assumption for your company website will be [your business name].com. Plus, .com’s generally have the most clout with Google and other search engines.
The .org extension is a very good choice for charity or non-profit sites, this is its most common use.
A .net extension would be the last choice of these 3 options. From the Search engine optimization end of things, .net is better than other extensions such as .tv, .info, etc.., but has lower google rankings weight than the matching .com and .org extensions.
Shorter names can be more helpful with marketing of your website and for people to remember and type into a browser.
Lastly, domain names should be thoughtfully planned. Changing your domain name after the website has been live for any length of time can lead to loss of SEO juice and also brand awareness from your marketing efforts.
Domain names are often seen in analogy to real estate in that domain names are foundations on which a website can be built, and the highest quality domain names, like sought-after real estate, tend to carry significant value, usually due to their online brand-building potential, use in advertising, search engine optimization, and many other criteria.
See this great article from seo.com (link below), for more information.