Any character with Extra Attack peaks specifically at level 5, though the half casters maintain better because of their spells. Monk gets a particularly strong peak at level 5 because of Stunning Strike, but then is the worst in upper tiers.

Rogue peaks in Tier 1.

Cleric and Druid peak in Tier 2 specifically because of their power spells, spirit guardians and conjure animals.

Wizards peak in Tier 4 because of wish. Also by that time they have all their high-level power spells: contingency, simulacrum, force cage… Wizards are peak.

Bards also get wish in Tier 4, but their curve is a bit flatter because they don't quite get all of the Wizard spells, and they get some useful stuff in the earlier tiers.

Sorcerer gets wish, though they might peak in Tier 2 because metamagic becomes extremely strong at that point.

Warlock probably peaks in Tier 2, when they establish whatever they're doing, and they have enough invocations and spells to be effective and versatile.

Actually Paladin peaks at level 6, with Aura of Protection