ZEUS
The thunder god is still king. Lightning Strike deals 10 damage at Common up to 20 at Heroic, and Thunder Flourish deals 30 at Common up to a crazy 60 at Heroic. That's just the base damage; Zeus's primary boons scale pretty well with poms.
Due to their flat damage, you prefer these boons on something that hits quickly. Lightning Strike is amazing on railgun, and Thunder Flourish on the bow (especially Chiron or Rama) is some of the best damage in the game.
If you take one of these boons, try to aim for Static Discharge, which adds Jolted to enemies struck by lightning. Jolted deals a large amount of damage when the enemy attacks. This also removes Jolted.
Nearly all of Zeus's support boons will help out the lightning effects in one way or another, but in particular, Double Strike (lightning bolt effects have a chance to strike twice) and the legendary Splitting Bolt (lightning effects create an additional burst) are very good. Cold Fusion, Zeus's Duo with Demeter, prevents Jolted from expiring when the enemy attacks, which can be very desirable for hit-and-run builds.
POSEIDON
Tempest Strike and Tempest Flourish are uninspiring at a glance: relatively low percentage damage bonuses (at Common, +30% and +70%, respectively) with a knockback effect that doesn't work against bosses. On top of that, the potency of the knockback effect varies wildly. It sounds like a great idea to stick Tempest Strike on the railgun so you can play keep-away with the denizens of the underworld, but the knockback on that particular combination is negligible.
But don't discount Poseidon. While the primary damage bonus is unremarkable, you can deal significant damage when knocking enemies into barriers, and there's no god in the game who's able to neutralize the entirety of Styx the way Poseidon does. These boons do best on big single attacks, like sword special or railgun special, because the knockback that is innate to those attacks will be amplified by Tempest Flourish.
Keep an eye out for Razor Shoals, which adds Rupture to foes affected by your knockback. Rupture deals some nice damage to foes that attempt to move. Breaking Wave (create a watery blast when you slam foes into barriers) turns Styx into pinball. Finally, Wave Pounding salvages Poseidon against bosses by increasing your damage against them when using Poseidon's knockback attacks, but the boost really isn't that incredible.
ARES
Curse of Agony and Curse of Pain apply Doom on attack and special, respectively. The Doom damage is roughly the same for both, with Curse of Pain dealing a bit more damage at Common and Rare.
This is flat damage, but whereas Zeus gives you a good reason to stick his flat damage on a fast attack, the non-stacking nature of Doom means Ares wants you to put it on something slower. Bow attack, sword special, and shield special are prime candidates. Shield special deserves a call-out because it easily spreads Doom across a wide number of targets with just enough cooldown to tag them right as Doom expires.
Most of Ares's boons are dedicated to blade rifts. He has two boons that improve Doom: Dire Misfortune increases the damage dealt when you apply extra Doom before it expires. The bonus damage is negligible, however. Impending Doom greatly increases the damage dealt by Doom at the cost of making it last half a second longer. This is usually very nice, but if you've gotten the timing down for reapplying Doom, then it can throw you off.
Two Duo boons deserve a special mention: Curse of Longing (Aphrodite) makes Doom continuously damage Weak foes, and Merciful End (Athena) makes your Deflect attacks instantly end Doom. With the right setup, Merciful End is the best DPS in the game, because Doom is the best flat damage in the game, and you can trigger it and reapply it continously.
DIONYSUS
"You thought it would be a useful god, but it was me, Dionysus!"
Drunken Strike and Drunken Flourish inflict Hangover, with Drunken Flourish dealing 1 more point of damage than Drunken Strike across the board. Hangover deals its damage every 0.5 seconds and lasts 4 seconds, so a single hit from a level 1 Heroic Drunken Flourish (8 damage) will deal 64 damage over 4 seconds.
Because it caps at 5 stacks, Hangover is fairly unimpressive compared to the more immediate effects you'll get from a god like Zeus. Recall that Zeus's Flourish deals 60 damage instantly, and you can keep piling that on instead of only being able to stick it on an enemy 5 times every 4 seconds. However, Hangover can get really good if you stack a lot of poms on it, because unlike most boons, it doesn't suffer from diminishing returns at higher levels. As with Zeus, you want your Hangover effects on something that hits relatively quickly, though since the damage is capped, you don't need to be that quick. Fists attack, spear attack, and railgun attack are decent candidates.
The advantage of Hangover compared to other damage sources is that it isn't stopped by armor. Big-damage attacks will get soaked entirely by the last point of armor on an enemy, but Hangover isn't bothered by that and will keep ticking.
I'm reaching a bit here. How can you keep Dionysus from being a poor man's Zeus? Other than stacking poms on your primary Hangover boon, keep a look out for a couple of Duos: Low Tolerance (Aphrodite) allows 8 stacks of Hangover on Weak foes, and Curse of Nausea (Ares) makes Hangover tick every .35 seconds, meaning each stack deals its damage 11 times instead of 8.
APHRODITE
Heartbreak Strike and Heartbreak Flourish are notable as the strongest percentage damage bonuses in the game. That alone is enough to recommend Aphrodite, but Weak is also good: -30% damage for 3 seconds. The additive stacking in the damage formula is true for penalties as well, so if you have another effect that reduces the damage you take by 20%, an enemy deals half as much damage when Weak. That's good!
Weak doesn't stack but can be reapplied, so Heartbreak is best on a high-damage attack that you expect to use often. Fists special and sword attack are prime candidates.
Be on the lookout for Broken Resolve, which increases the damage reduction from Weak, and Empty Inside, which greatly increases the duration of Weak. The Legendary Unhealthy Fixation gives Weak effects a 15% chance to Charm as well, which is just ridiculously good.
DEMETER
Frost Strike and Frost Flourish are percentage damage as well and nearly as strong as Aphrodite's equivalents. The big difference is that Chill stacks and Weak does not. You can still treat Demeter like Aphrodite, but I find there's more value in stacking up Chill. Railgun attack and bow special are very good candidates for this.
Having an enemy slowed is its own reward, but Arctic Blast is a game-changer: when you max out Chill, you create a high-damage blast that wipes out all Chill stacks. This lets you treat Demeter more like Zeus than Aphrodite, and any slow effects you get on the way are icing on the cake. Of course, you'll want your build to work without Arctic Blast, because you can never guarantee any given boon, but Arctic Blast turns Demeter from support to primary source of damage.
ATHENA
Divine Strike and Divine Flourish are middling percentage bonuses that add Deflect to your attack or special.
...I'll be honest here: I take Divine Dash 100% of the time and Strike/Flourish approximately 0. For Athena, I defer to Kalir:
ARTEMIS
I've saved the best for last! Artemis has the lowest percentage bonuses in the game. Deadly Strike gives a 15% chance to deal Critical damage, and Deadly Flourish gives a +20% chance to deal Critical damage.
Critical triples the total damage of an attack. It's time for some math. For simplicity, let's say you've got an attack that deals 100 damage. In one corner, we've got Aphrodite, willing to give you +80% damage, which is a simple 180 damage on every hit. In the other, Artemis is offering +40% damage with a 15% critical rate. 85% of the time, that's 140 damage, and the other 15%, it's 420. On average, that's 182 damage.
So Artemis is about the same expected damage, and Aphrodite gives you a nice status effect to boot. What's the big deal?
The big deal, it turns out, is that there are a lot of percentage damage boosts in the game. Back attacks, boiling blood, Pierced Butterfly, Urge to Kill, Chaos boons, whatever. And they all stack additively until you throw Critical into the mix. Critical takes the final damage of the attack and triples it, and it's the only effect that manages to beat additive stacking.
The temptation is to stick this on a single, big boom, like railgun special. You're going to be better off putting it on whatever is your primary source of damage, though, which is usually your attack. If your primary damage is your special, even better: Deadly Flourish has a markedly higher critical rate.
While the baseline on Critical is +200% damage (multiplicative with other bonuses!), Clean Kill and the Duo boon Heart Rend (Aphrodite) can increase that number additively. Hide Breaker is another enormous +200% at the Common level, but it only works against armor, and a single critical hit is usually enough to strip a foe of its armor.
Bigger than damage increases, however, are opportunities to increase your Critical chance. Nemesis sword and Zagreus bow each have innate Critical, and Pressure Points gives every source of damage you deal a chance to crit. The Duo boon Deadly Reversal (Athena) gives a whopping +20% chance for 2 seconds after you Deflect, and Splitting Headache (Dionysus) gives +1.5% per Hangover stack.
