What is the brand of the device used by the most users in the M23-26 user group?
brand of the device refers to phone_brand; M23-26 user group refers to `group` = 'M23-26';
SELECT T.phone_brand FROM ( SELECT T2.phone_brand, COUNT(T1.device_id) AS num FROM gender_age AS T1 INNER JOIN phone_brand_device_model2 AS T2 ON T1.device_id = T2.device_id WHERE T1.`group` = 'M23-26' GROUP BY T2.phone_brand ) AS T ORDER BY T.num DESC LIMIT 1