[ZFanatic88]

kali is the most common, it has good preinstalled tools, if you are starting it is very good, then you can try other distributions and see which one you like more, but I vote for kali.

[N1k7]

Qubes OS > solid choice.

Has everything that you need and is very much well liked by Linux community. Kali is great for only pen test purposes, Qubes if set up right can give better results.

[breachxyz]

for me any .deb distribution would be fine i prefer ubuntu GUI , but kali linux has pre-installed tools that helps you