Hey welcome Dave.
Id first say the answer is buy what you like. If you like the look of his 40PB, no real reason to pass on it and buy a 39 just because people may tell you to.
Or vice versa.
Now if resale is a concern, the more popular issues typically are easier to sell.
I'm a collector and personally speaking when I buy a card because I like it, I never regret it. I liked it. What can be bad?
So follow your gut.
And to answer your specific question, I'd take the SGC 70 of whichever PB had the best clarity and centering. Sgc cuz I like their flips.
Good luck. Welcome!
Peter