Easily the Rise of Darkrai or Lucario and the Mystery of Mew.
Lucario and the Mystery of Mew is such a powerful movie, it involves friendship, selflessness, and sacrifice.
I honestly can't watch it without crying, the beautiful song at the end brings the tears, as does Lucario's demise. I just love everything about the movie, it gives me so much nostalgia. The overall message of the movie truly stands out to me and is very impactful.
The Rise of Darkrai is another favourite, and another movie that brings about tears. I love Alice, Tonio, and other characters that are introduced. The design of Aloamos town itself is stunning, and Oracion and the soundtrack is just so spectacular. The lyrics in 'I'll Always Remember You' touch my heart, and fill me with so much emotion.
Both of these have so much depth to them which I think more recent movies lack.