Whisk mayonnaise and sour cream in a bowl until smooth and creamy.
Stream in the buttermilk while whisking until it reaches your desired thickness.
Stir in parsley, dill, chives, onion powder, garlic powder, pepper, and salt until well blended.
Add lemon juice, vinegar, and sugar. Taste and adjust salt and pepper as needed.
Cover and chill for at least 20 minutes before serving to let the flavors meld.