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