Worked out · Valheim 1.0.17

Best atgeirs

All Valheim atgeirs (polearms) ranked by damage at max level, damage per stamina over a full combo and the secondary attack, and the best one you can make in each biome.

Strongest atgeir
Frostfire AtgeirAtgeir
296damage
Most damage per stamina
Frostfire Atgeir3-hit combo
19.7per stamina
Hardest secondary attack
Frostfire Atgeir× 1 for 40 stamina
296damage
First you can make
Bronze Atgeir63 damage at max level
Black Forest

Best atgeir in each biome

Of the atgeirs you can make by then, the one that kills the biome's hostile creatures in the fewest hits, their weaknesses and resistances applied (every weapon by biome).

Biome	Best atgeir	Hits	Creatures
Black Forest	Bronze AtgeirPierce	40	5
Swamp	Iron AtgeirPierce	79	9
Mountains	Iron AtgeirPierce	38	4
Plains	Black Metal AtgeirPierce	54	5
Mistlands	HimminaflPierce + Lightning	46	6
Ashlands	HimminaflPierce + Lightning	74	9
Deep North	Thunderblood AtgeirPierce + Lightning	76	9

All 7 ranked

Atgeir	From	Damage	Per stamina	Secondary	Stamina	Block
Frostfire Atgeir178 Pierce21 Fire97 Frost	Deep North	296	19.7	296×1	20	88
Thunderblood Atgeir222 Pierce60 Lightning	Deep North	282	18.8	282×1	20	88
Nord Atgeir212 Pierce	Deep North	212	14.1	212×1	20	88
Himminafl85 Pierce58 Lightning	Mistlands	143	9.5	143×1	20	64
Black Metal Atgeir123 Pierce	Plains	123	9.1	123×1	18	52
Iron Atgeir83 Pierce	Swamp	83	7.9	83×1	14	28
Bronze Atgeir63 Pierce	Black Forest	63	7	63×1	12	16

Formula

Damage at max level = base + per level × (max level − 1), each damage type apart; chop and pickaxe left out of the rating (almost every creature ignores them).

Full combo = (combo hits − 1) × hit + hit × the last swing's multiplier; per stamina = combo damage ÷ (stamina × combo hits). Secondary attack = hit × its multiplier.

Stamina and eitr per attack are at skill 0; skill 100 takes a third off (× 0.67) for every weapon alike, so the order doesn't change.

ItemData.GetDamage, Attack.DoMeleeAttack / FireProjectileBurst, Attack.GetAttackStamina, HitData.ApplyResistance in the code of Valheim 1.0.17.

Assumptions

Skill 50 in the weapon's skill, weapons at their max normal level, no stars on the creatures (a star doubles health, two stars triple it).
Every hit lands and only the primary attack is used; no backstab, no stagger bonus, no armor set or mead bonuses.
Area hits (staffs, sledges, atgeirs) are counted against one creature at a time.
Bows and crossbows fire the best arrow or bolt for the target you can make by then, at full draw.