Hadrat Anas bin Malik (r.a.) reported: ‘The supplication most often recited by the Prophet (saws) was: "Allahumma atina fid-dunya hasanatan, wa fil-akhirati hasanatan, wa qina adhaab-annar (O our Lord! Give us in this world that which is good and in the Hereafter that which is good, and save us from the punishment of the Fire)."'
Related by Bukhari and Muslim. Hadith quoted from Riyad-us-Saliheen
The Messenger of Allah (saws) preferred to make supplications which were short and general in nature; and there is no better supplication one can make than beseeching the Lord Most Gracious to bestow upon them good in this world, good in the Hereafter, and safety from the punishment of the Hell Fire.
It is reported that the Messenger of Allah (saws) would recite this supplication more often than any other supplication.