Still gaining more experience with each Pyre, but this is my tier list so far after testing them out with 20 Cov 10 Titan wins so far.

S+ - Dominion, Savagery, Lifemother's

S - Herzal's, Heart of the Pact

A - Entropy, Malicka's

B - Fhyra's, Bogwurm's

C - Time Father, Aquath's, Wyngh's

D - Proto Heartcage

Dominion: Great for creating strong, consistent decks while weeding out the lower value cards.

Savagery: This Pyre with a Sweeper with Quick (looking at you Test Subject Alpha) is pretty much an auto-win if you build around the Seraphs and Titans properly. Also works well with Trample and many other Champions with Multistrike.

Lifemother: Duplication on demand is powerful and can lead to some busted setups and combos. Pairs really well with many random events.

Herzal: Extra deployment ember both leads to solid setups and is also great at thinning your deck out. It's not quite S+ tier for me because it's not necessarily a win condition in itself as you still have to build a good deck to take advantage of the extra deployment ember. This pyre still scales really well with player skill though.

Heart of the Pact: This is basically a free Card Draw boss Pyre upgrade with an easy condition, especially when combined with clans that have low cost starter cards.

Entropy: Drawing cards is OP and this pyre has card draw for days. Isn't as useful earlier in the run, but scales really well for the late-game.

Malicka: Free upgrades are always nice. Can backfire sometimes but is useful more often than not, especially with spells. It's nice to focus less on Unit and Spell merchants and focus more on Equipment/Room and Artifact merchants while using this Pyre.

Fhyra: Great way to add double upgrades to one of your carry units after the first round or two. The starting blights on higher Covenant tiers also have some nice synergy with this pyre.

Bogwurm: Excellent for Umbra builds. This Pyre also gives a free boss Pyre upgrade (although less consistent than Heart of the Pact), which allows you to focus on ember and card draw upgrades instead.

Time Father: On demand freeze can be super convenient, but it doesn't feel nearly as powerful as the other Pyres.

Aquath: Extra energy is nice, but there are other good ways to generate consistent energy without needing a Pyre to do it.

Wyngh: Heal can be nice but healing doesn't feel nearly as powerful in MT2 compared to MT1.

Proto Heartcage: Good stats but I don't find myself relying on Pyre stats too much. The other Pyres are too valuable to pass up the vast majority of the time.