I pick .com for everything. .net for network related things but only associated with the .com (CDN cookieless domains, etc).<p>I'm ok with .tv and .io domains for specific things.
.[country code] for localized content regardless of what it is<p>.com - For selling stuff<p>.net - Communities / free services<p>.io - for dev and html5 game stuff
.org when projects seem sufficiently serious<p>.xyz when it's an alpha, beta or testing project<p>.com when it's meant for silly or stupid things