Which artist has released the most singles with the tag "soul"?
the most singles refer to MAX(COUNT(releaseType = 'single'));
SELECT T1.artist FROM torrents AS T1 INNER JOIN tags AS T2 ON T1.id = T2.id WHERE T2.tag = 'soul' AND T1.releaseType = 'single' GROUP BY T1.artist ORDER BY COUNT(T1.releaseType) DESC LIMIT 1