What is the simplest known NP-Complete problem for testing P=NP solutions? [closed]

About a year and a half ago I ask this question regarding $P=NP$. The answers have helped me understand the problem tremendously and since then I've dabbled further into the topic.

With that stated, it is my understanding that $NP-Complete$ problems are such that if a solution for $P=NP$ were found for that specific problem, then all $NP$ problems could be solved using the same rules for resolving $NP$.