Does a latecomer, when his imam says the taslim, say, “Allah hears the one who praises Him; our Lord, to You be praise,” or does he suffice with saying only, “Our Lord, to You be praise,” mentioning the opinions of the four schools of thought and the preferred view?

The latecomer, after his Imam's salutation, takes the ruling of an individual because the following (of the Imam) has ceased. Therefore, the latecomer says "Sami‘a Allahu liman hamidah" (Allah hears the one who praises Him) upon rising from bowing, and "Rabbana wa laka al-hamd" (Our Lord, and to You be all praise) after standing upright from it.