Try this:
MySQL
SELECT A.name, COUNT(A.name) nameCnt
FROM (SELECT C.Name
FROM Product P
INNER JOIN ProductCategory PC ON PC.PID=P.PID
INNER JOIN ProductMaterial PM ON PM.PID=P.PID
INNER JOIN Category C ON C.NodeId=PC.CID
WHERE PID IN('2233','4432','5665','1252')
GROUP BY PC.CID, PM.MID, C.DanishName
) AS A
GROUP BY A.name
ORDER BY nameCnt DESC LIMIT 1;
SQL Server
SELECT TOP 1 A.name, COUNT(A.name) nameCnt
FROM (SELECT C.Name
FROM Product P
INNER JOIN ProductCategory PC ON PC.PID=P.PID
INNER JOIN ProductMaterial PM ON PM.PID=P.PID
INNER JOIN Category C ON C.NodeId=PC.CID
WHERE PID IN('2233','4432','5665','1252')
GROUP BY PC.CID, PM.MID, C.DanishName
) AS A
GROUP BY A.name
ORDER BY nameCnt DESC;