I am inclined to suggest that Patronage is probably the most powerful of all of the policy trees. But there are two very important qualifiers: 1) Difficulty level and 2) the number of City States. I really can't say just how things differ up there in Diety-land because the highest I've gone is only King (my current game). And when doing setup I always have a Huge map with all 41 CSs in play, playing at Marathon speed. Inside that criteria, I pretty much dominate by the end of the Renaissance, mainly because I'm Friendly with all 41 CSs, with most of them being Allies. As such, for the entire game, I've never actually built more than a dozen units -- yet I have THE most powerful Military because of all the units the Militaristic CSs send me. I'm also the Faith leader by a very large margin because of the Religious CSs contributions, as well as the Culture leader because of the Cultured CSs sending me Culture points. And the empire is happy as clams because the Commerce CSs sending us Happy points. And Food is no concern because of all the groceries the Maritime CSs contribute. Plus, because I fleshed out the Patronage tree, I'm getting several hundred Research points every turn, along with occasional (more often than "rare") Great People units.
Policy-wise, the first tree I do complete is Patronage. But I also at least initiate practically every other tree as well. I eventually fully complete Commerce (for healthy cashflow), and perhaps Piety (to get the Reformation Belief, and being that close might as well take the last one to complete the tree). Then I cherry-pick certain useful policies from the other trees until Ideology kicks in. The reason I have been able to adopt sooooo many policies is because, beside the CS contributions, I really focus on completing those Wonders and techs that bestow free Social policies. That's between 6 and 12 extra policies where I didn't need to pile on the Culture points AND drive up the per policy price. There are also several things that can reduce Culture costs by 10-33%. If you're paying close attention, it's all quite doable.
This game, I disabled both the Domination and Diplomacy Victories because if I didn't the game would be over -- like all the others before it -- by @1950. And if I enabled the Diplo Victory, because of my total control of the World Congress, I'd be World Leader in the 1800s, at the latest.
And I attribute all that to Patronage.