Don't use the `comments` table: it was last updated December 2017.

On the full table:

    #standardSQL
    SELECT
     `by`,
     COUNT(DISTINCT id) as `num_comments`
    FROM `bigquery-public-data.hacker_news.full`
    WHERE id IS NOT NULL AND `by` != ''
    AND type='comment'
    GROUP BY 1
    ORDER BY num_comments DESC
    LIMIT 100

tptacek is in first place with 47283 comments.