According to islamqa.info the du'a
“Allaahumma laka sumtu waswa ‘ala rizqika aftartu (O Allaah, for You I have fasted and by Your provision I have broken the fast)"
is weak but this is hasan
“Dhahaba al-zamau’a, wa abtallat al-‘urooq wa thabata al-ajr insha Allah (Thirst has gone, the veins are moist, and the reward is assured, if Allaah wills).”
Is this correct as the former is very popular in masjid and literature.
Also if you read the meaning carefully you should break the fast first then say the du'a - "...broken the fast..." this is past tense. Also "...thirst has gone..." Again past tense meaning you have broken the fast and then say du'a. Most people do the reverse. Please comment.