In a large bowl, combine tomatoes (undrained), onion, garlic, cilantro, and sugar. Mix well. Blend approximately half of the tomato mixture by placing spoonfuls into a blender and covering with broth. Blend until smooth. Pour into large pot. Place remaining mixture in pot with remaining chicken broth. Add chicken and chipotle peppers. Bring to a boil, reduce heat, and cover. Simmer for approximately 20 minutes, or longer.
Put crushed tortilla chips in bowl and cover with soup. Top with shredded cheese, avocados and sour cream, as desired. Serve immediately.