Small update: I got my first CGC graded Spider-Man #252, my 12th copy over all.
Decided to read back through this thread, found it interesting how some people were saying that opinions didn't matter, then saying that it is obvious that 252 is the first appearance. (Which I agree with)
And yet, them saying this is them expressing their opinions.
I found it interesting, though, that majority of people voted that #252 was the first appearance. When the book increases in value over time, that book will be the one that experiences the most growth.
I am glad I never bought a PPSM #90, though.