How have the rules in Tasha's changed racial optimization? What are the best races for different classes under the new rules? For example, I would argue that Tortles are now the best race for wizards and warlocks?
I am interested in what the community thinks. Thanks.
It depends on what you mean by "best" if you are considering all 3 pillars there is a strong argument that Humans, Mountain Dwarves and PHB half-elves are the best races for all classes. Also shifters are strong for any class.
If you are talking about combat specifically and not including flying races here is how I see it (note this includes Fizban's and ability to swap weapon proficiencies too):
Artificer: Goblin
Barbarian: Bugbear, Goblin, Orc, Half Orc, Dwarf, Yuan-Ti, Human, Custom
Bard: Goblin
Cleric: Goblin
Druid: Goblin
Fighter: Bugbear, Kobold, Goblin, Yuan-Ti, Hexblood, Human, Custom
Monk: Tortle, Hexblood, Kobold
Paladin: Dragonborn, Goblin, Kobold, Bugbear, Yuan-Ti, Hexblood, Human, Custom
Ranger: Dragonborn, Goblin, Kobold
Rogue: Bugbear, Kobold, Lightfoot Halfling, Wood Elf
Sorcerer: Goblin, Human, Custom
Warlock: Dwarf, Gith, Goblin, Human, Custom
Wizard: Elf, Dwarf, Gith, Goblin, Human, Custom