The optimal way to pray a 3-rakat witr is:
(1) To pray two rakats of the witr prayer and give salams, and then to stand up and pray one rakat of the witr prayer and give salams.
(2) To recite Surat al-A'la in the first rakat, Surat al-Kafirun in the second rakat, and Surat al-Ikhlas, Surat al-Falaq and Surat al-Nas in the last rakat (so one recites a sura after the fatiha in all three rakats).
Many Shafi'is said that it is disliked to pray the 3-rakat witr with only one salam (because of a sahih hadith that says not to make the witr prayer resemble the maghrib prayer), but if one does, then it is superior to confine oneself to a single testification in the final rakat.
(Tuhfat al-Muhtaj, 2.227)
And Allah knows best.