Free Agent - NA
This is all from my perspective from my experience playing on NA mouse & keyboard queues. The popularity and potential of all the gods in smite is of course going to vary depending on what platform and region you play on. If you truly don't understand how a god can be ranked so highly the answer most likely has to do with it's synergy with the two strongest starters in duel right now. You can also ask me to try and explain it better to you on stream.
SO TL:DR
This is all my opinion and a lot of gods are rated higher than you would expect due to Manikin Scepter and/or Bumba's Hammer abuse. These items are OP and drastically shift the potential of a lot of gods.
ss
Every god in SMITE can be beat but I would have to say Ullr has the most winning match ups out of any god.
s+
Gods most people should be picking or banning. These gods should not lose very often unless versus other gods in adjacent tiers.
s
Gods that should be picked or banned a lot but not nearly as much as the gods above S.
s-
Gods that generally don't get banned but have a lot of winning match ups even against some of the gods above them.
a+
Gods that are above average and can have a lot of decent match ups against gods higher tier than them but generally don't win against majority of the top picks.
a
Gods that are very average and can actually have some decent odd ball match ups against some of the top tiers. That being said, I would generally avoid these gods if your goal is to win.
a-
These gods are not hopeless and can get wins but generally I would avoid them if your goal is to win.
b
Bad
c
Really Bad