A very common question I get when working with a new client is, does it matter if they choose .com, .org, or .net as their domain name extension and the answer is not exactly yes or no.
The short answer is no. But that is in regards to ranking and optimization. When you build a strong website and ensure you cross all your T's and dot your I's, ranking is ranking regardless of your extension.
Where your domain extension matters is in what your target market is accustom to. I can only really speak to what the standard is in the U.S. as far as what extensions imply on a domain name. So if your market is in France or India this information won't apply.
The most commonly known and favorite extension is .com and it is what most people will gravitate to when given a choice as a domain name. Basically, your first go to for an extension is .com for most industries.
If you're a tech company or a health and wellness website that cannot get the .com you want you can make the shift to .net and it will still flow nicely and fit the norm.
.org is great for non-profits, educational sites, city and government websites (if they don't use .gov) and medical sites.
My advice is if you can, buy them all. This will help with S.E.O and keep your domain name out of the hands of others. It is not difficult to have multiple domain names point to the same site and the cost of most domain names is fairly inexpensive my personal preference to purchase domains is Godaddy. They are not the cheapest but as far as customer support and ease of use it is my favorite.