In the spirit of brazen discussion and ranking of the various aspects of the game, I present to you my (rough) opinion on overall boon rankings in this game:
Top Tier
The very juiciest, most wonderful awesome boons out there. Deities with even one such boon are superb picks.
Absolution
Body Pact
Humility
Blood Tithe
Boost Health
Boost Mana
Stone Heart
Consensus
High Tier
While a notch below the best boons, these are still highly respectable and great choices in almost any scenario.
Chaos Avatar
Poison
Blood Shield
Blood Swell
Tikki's Edge
Reflexes
Warrior's Pact
Last Chance
Mid Tier
This is the middle-of-the-road stuff. The bread and butter of boons. All well worth your time, but not worth going too far out of your way for.
Dodging
Magic
Stone Skin
Unstoppable Fury
Blood Hunger
Stone Fist
Spirit Pact
Scholar's Pact
Low Tier
While not bad, per say, these are clearly sub-par boons. They're worth your time if nothing better is available or if they're well-suited to your current situation, but generally offer too little to be worthwhile if there are better offerings on the table.
Taurog's Helm
Taurog's Armor
Stone Form
Vine Form
Entanglement
Taurog's Blade
Refreshment
Alchemist's Pact
Bottom Tier
While “crap” is a strong word, these boons are either overpriced, underwhelming, or too double-edged for serious consideration. In the right circumstances on the right character they work and none of these are useless, but they aren't ideal ways to spend your hard-earned piety.
Protection
Enlightenment
Cleansing
Weakening
Flames
Taurog's Shield
Greenblood
Not Rated
These boons are either used to control a deity's downsides or else are exclusively used to generate piety with a chosen deity. As a result, I do not regard them as stand-alone boons but rather as part of the baggage that comes with a deity. They are factored into my rankings of the other boons provided by their respective deities, just as piety generation and on-worship effects are. The sole exception to this rule is Consensus, since it can be applied to any deity and precludes pacts. Mystic Balance is not rated because I'm presuming it's going to be completely reworked in the near future.
Clearance
Plantation
Blood Curse
Petition
Stone Soup
Mystic Balance
Tribute
Open for discussion