My personal pick of gods that are the best to play/most frustrating to fight against, taking into account the modes I play, which is basically everything but Conquest and Siege.
At this time, I don't think there is any one god in the game that is SS tier.
Gilgamesh is just here until further notice.
These gods excel in everything they do and have the upmost potential to turn around fights. It doesn't matter what you're doing - you just have to hope the person playing them sucks.
These gods are very strong and fit into all comps, but they're not as strong as the S+ gods.
These gods are strong, but have some sort of hinderance or skill ceiling with their kit that interferes with them being a higher tier (no/situational ult, missing abilities = useless, Kaldr dying quickly/Skadi's ult constantly bugging out, etc)
With the right player/team however, these gods excel greatly when they're able to do what they're supposed to do.
Cream of the crop gods. They aren't spectacular or horrible enough to be above or below this tier, so here they are.
These gods are somewhat situational but all have the potential to carry their team in terms of damage or peel. A lot of them are easily countered but also pumps out lots of damage that can be devastating to the other team.
These are situational gods that aren't as bad as the tiers below, but there are better choices. Some of them have a skill ceiling that is hard to reach, which hinders their standing.
Freya in Duel being the exception.
These gods are pretty situational, and many are downright boring to play. Repetitive, some useless, and easily avoided abilities - a lot of them are also unsafe to play in most match ups.
Thanatos/Mercury are the exceptions; a skilled player will likely dominate with them, but that's hard to come by.
These gods are VERY situational in most matches - ironically, these 3 are great/decent in Duel, not so much in other modes unless the player is highly skilled with them.
There's no point or merit with playing these gods. There are over 100 other gods in the game to choose from; do yourself a favor and don't choose them.
Ah Puch: low mobility, predictable ability pattern that doesn't change and can be avoided easily, is more of a liability for the team
Bastet: useless passive, weak kittens/lost ability to backdoor, predictable jump back, countered easily by many of the newer gods' CCs e.g. stuns/roots