What is the best penetration testing tool?

the best penetration tool is Nmap

May be it is Wireshark......

Not a very big fan of Ethical Hacking.

In Practical Life, and in my opinion  MSF Framework (Metasploit Framework) is the Best Tool especially if your a programmer

I would say collection of tools and Technics.

I would recommend using Kali Linux and  inside tools for recon/pen test. 

I would recommend Metasploit frame work.