How many visitors you will receive is not depend on the domain extension but on your keyword use on that domain and not forget the contents of your site. Just like what others said, go for .com because that is the most recognizable domain extension in the world. If you have money to spend, purchase all other extension too for that domain for branding or trademark purpose. - Dynashox -
I would suggest .com unless you have a specific reason to choose a different TLD. For example if you were targetting the German Google search you would want to opt for a .de.
I would tend to agree that the .com extension is the most popular. However, I recently registered 2 identical domain names; one with .com and the other with .cn. To my greatest surprise my .cn website immediately got Alexa ranking and acquired Google Indexed pages much faster than the .com.