which one for me?

Hi all. I have recently learned Series 90 of GS. I notice that no one talks about this version. Perhaps because it's not very effective when it comes to speed...??! I am about to start studies on Diamond Jubilee and perhaps Simplified. I wonder, which version out of all six has what benefits and disadvantages? And I've also noticed that no one seems to talk about Centennial. Why is that? Isn't that the most recent one? 

(by misssuzzette for everyone)