Which Pentesting OS Is the Best?

So i would like your opinion on this...

Which pentesting OS is the best?

I have toyed around with kali and backbox (and just a little bit with parrot os) and i don't know which one is better,i would use them all but i cant due to my crappy laptop so i can only choose one!

EDIT: If you had to choose one, which one would it be?