What PHP version do you use?

WordPress PHP requirement is easy. PHP 5.2.x is the minimal version, maybe because it supports JSON natively, however WordPress team recommend PHP 5.4. You must know, that PHP 5.3 is obsolete and it is no longer supported. It was alive since 30th June 2009 (sic!) to 14th August 2015.
What brings PHP 5.3 so useful?
Namespaces. Of course there are a lot more. But for our WordPress adventures, we do need namespaces. Because it is the way to omit any name conflict.
So, I can recommend you at least PHP 5.5 (it started on 20th June 2013!) and my themes / plugins requires PHP 5.3 at least (because it uses namespaces). If your host provider doesn’t support PHP 5.3 (yes, there are some geeks like that) then say goodbye to them. They sucks.