It is said that the important night of Qadr is one of the odd nights of the last ten days of the holy month of Ramadhan. The night of the 19th, 21nd, 23rd, 25th, 27th, 29th. The emphasised nights are the nights of the 19th, 21st and in particular the night of the 23rd.
As for the night of the 27th, athough it has also been mentioned in Shi'ah narrations, it is the night usually emphasised on by our Sunni brethren.
And Allah knows best.