Half-Elf is good for a Hexblade with Pact of the Blade, as its racial bonuses can give you very high Charisma to use as a modifier with Hex Warrior. Aasimar also get +2 Charisma boost and have a strong roleplaying link with an otherworldly patron. If you want to use Strength as your Warlock’s modifier, Dragonborn get a Strength boost.