"Which is best operating system for my PC of linux versions?"
That depends on a few factors: your computer's hardware, your individual needs/workflow, and your familiarity with Linux-based systems. Arch or Gentoo may fly on your PC, but if you're a newbie who doesn't know what a repository *is*, let alone how to add or remove one, it's a moot point, you're in way over your head.
"can i order delivery for free CDs or DVDs of Linux with versions?"
I don't think any distro offers free installation discs/USB sticks any longer; Canonical ended it's prominent "Ship It" program a year ago, costs were simply too high. There are vendors which sell Linux discs, but frankly downloading, burning, and installing them yourself is easy, and provides an example of how tech support the "Linux Way" is done: research your options, decide, and if you run into trouble, Google and the forums are your best friend.
There's a reason so many Linux distros exist: different users have different wants/needs, the large variety of choices cater to the userbase. The best Linux distro is the one that works best for you.