Imam anNawawi (radiyAllahu `anhu) was once asked, while at a Masjid in Damascus, "does sending peace and blessings upon the Prophet sallAllahu `alayhi wasallam receive a greater reward than the Obligatory Prayers that God the Most High has ordered us to perform?"
Imam anNawawi went silent for a few minutes and then replied, "the prayers upon the Prophet sallAllahu `alayhi wasallam (are greater in reward)".
The questioner asked, "how did you arrive at this? For verily God the Most High has obligated this obligation upon His servants; how can something else be greater (than this)?"
So the Imam replied, "Yes, He obligated upon you five prayers in a day and he obligated you with sending prayers and blessings upon the Messenger of God sallAllahu `alayhi wasallam with His Saying, 'Verily God and His Angels send their peace upon the Prophet; O you who believe, send upon him your peace and peaceful salutations.' So this is an obvious obligation, for you are between two obligations, the obligation of prayer and sending peace upon the Prophet sallAllahu `alayhi wasallam."
So the questioner went silent for a short while, then said, "then they are equal."
"No," said the Imam, "an obligation ordered upon you by God does not compare to an obligation that God and His Angels and His servants perform, too; it is greater than the obligations that you perform by yourself."
--- From the book, The Safeguarding Path to God in the time of the Dajjal and the Mahdi" of Hasan alWakil
اللَّهُمَّ صَل عَلَى سَيِّدِنَا مُحَمَّدٍ ۞ الفَاتِحِ لِمَا أُغْلِقَ ۞ وَالخَاتِمِ لِمَا سَبَقَ ۞ نَاصِرِ الحَقِّ بِالحَقِّ ۞ وَالهَادِي إِلَى صِرَاطِكَ المُسْتَقِيمِ ۞ وَعَلَى آلِهِ حَقَّ قَدْرِهِ وَمِقْدَارِهِ العَظِيمِ ۩