Get data from both tables what join should I use
Simply, you can use a CTE or SubQuery then ORDER BY [T1.T2] DESC as

WITH CTE AS
(
  SELECT Col1, Col2, 'T1' [T1.T2]
  FROM T1
  UNION
  SELECT Col1, Col2, 'T2'
  FROM T2
)
SELECT *
FROM CTE
ORDER BY [T1.T2] DESC;


Live Demo