This will sort records in descending order by date, keeping the Archive records at the bottom:
SELECT c
FROM MyBundle:Category c
ORDER BY case when c.name = 'Archive' then 2 else 1 end,
c.createdAt DESC
As an extension to this answer, this is what I had to change to make it work with DQL:
SELECT c,
CASE WHEN c.name = 'Archive' THEN 2 ELSE 1 END AS HIDDEN sortCondition
FROM MyBundle:Category c ORDER BY sortCondition, c.createdAt DESC