Well, 'The Boy in the Striped Pyjamas' is among the best holocaust novels. This novel shows the Holocaust from a unique perspective of a young boy who befriends a boy in a concentration camp without fully understanding the horror around him. 'Maus' by Art Spiegelman is also excellent. It's a graphic novel that uses animals to represent different groups, making the story accessible yet deeply moving. And 'All But My Life' by Gerda Weissmann Klein is a powerful memoir of her survival during the Holocaust.
One of the best is 'The Diary of a Young Girl' by Anne Frank. It gives a very personal and poignant account of a young girl's experience hiding from the Nazis during the Holocaust. Another great one is 'Night' by Elie Wiesel. It's a harrowing memoir that vividly depicts the atrocities Wiesel endured in the concentration camps. Also, 'Schindler's Ark' by Thomas Keneally is notable. It tells the story of Oskar Schindler who saved many Jews during the Holocaust.
Definitely 'The Tattooist of Auschwitz' is a great holocaust novel. It's based on the true story of Lale Sokolov, a Slovakian Jew who was forced to tattoo the prisoners in Auschwitz. It shows his love story with Gita in the midst of the horror. 'If This Is a Man' by Primo Levi is also a very important work. Levi's account of his time in Auschwitz is a searing exploration of the dehumanization in the camps. 'Suite Française' by Irène Némirovsky, although not solely about the Holocaust, still gives insights into the period as Némirovsky was a Jewish writer writing during the Nazi occupation of France.