Though this is mostly my opinion I think that most of you can agree with most of the placements on this list. Some are bordering between the lines so keep that in mind. If you think something should have been A+ but is only A chances are it was somewhere in between and I decided to put it in A.
Now that that's out of the way, this list was based off of a few factors:
1: Pick/Ban Rate. Some of the gods like Ah Muzen Cab are banned nearly every game and clearly outperform a lot of other lower ranked gods while Kali, though this list is my opinion, is S- simply because of her ban rate and I face no difficulties against her.
2: Performance. An example would be Poseidon and Anhur. They both perform on-par, if not, better than Ah Muzen Cab in a lot of match-ups but they are ranked lower simply because of the lower ban rate.
3: Counter Match-ups. An example of this would be Loki. A strong god if faced against the right match up but often times rendered helpless in many match-ups due to shields, burst, counter ults, etc. Though he can win by running around an entire match in a counter-match this is only viable if the opponent isn't patient. If he plays against any of the top tier gods EXCEPT Ah Muzen Cab, it's almost a surefire loss. Another example would be He Bo because of his lack of counters but I'm not getting into detail about that.

A lot of the lower tier gods, namely the B tier gods, I wish I could place higher up but simply because of the typical performance and lack of good match-ups I have to leave them there. I was debating on putting Odin in A- but simply because there are many items that can counter his burst and auto him down afterwards he is put in B.