The Night of Qadr according to most authentic Hadeeths is 19th or 21st or 23rd of the Month of Ramadan.
Most of our brothers and sisters who follow Sunni sects think that 27th is the most likely night of Qadr. This is because of the Sunni rulers who wanted to drive the Muslims away from the narrations and teachings of Ahlul Bayt (AS).
In fact, there are many authentic Hadeeths in Sunni books stating that the Night of Al-Qadr is 19th or 21st or 23rd. (Nayl Al-Awtaar by Al-Shawkani).
The narration of 27th is unauthentic narration which has been narrated by one person named Ubayy Bin Ka'b stating his own opinion and not narrated from the Prophet Muhammad (SAWA) but it was been publicized by the rulers against the authentic Hadeeths from Ahlul Bayt (AS).