Thermal Compound stock or should i buy some

That depends. What stock paste are you referring to?
Coolermaster paste is good, so is corsairs factory paste. AMD and intels paste arent as good, but they are far from bad.

Honestly for the price you might as well get paste though, it can lower temps a few C, which isnt much, but it can make a difference.
AS-5 is well know, very well known. But I recommend Arctic MX-4
 
The paste that comes with most heatsinks is fine and the difference is usually a few degrees at most. If you intend to push a high overclock though it won't hurt.

Artic silver 5 is not a modern paste or a very good choice. Its not awful but its been 10 years since it was a great choice.

www.tomshardware.com/reviews/thermal-paste-performance-benchmark,3616-7.html
 


But if you read the conclusion it actually says that they can't decide on it, so a arctic silver 5 will do fine unless you plan on doing some crazy overclocking