What is the ruling on one who performs the obligatory prayers but does not observe the Sunnah prayers, and is there a difference between the Sunnah prayers of the five daily prayers, or are they all equal?

Allah has mandated five daily prayers, which are the distinguishing line between Muslims and disbelievers. Whoever abandons them has disbelieved. Furthermore, the first thing a servant will be held accountable for is prayer. If there is any deficiency in the obligatory prayers, it will be completed by supererogatory prayers, out of Allah's mercy for His servants. Negligence regarding supererogatory prayers should be avoided because they complete what is lacking in the obligatory prayers, especially at the time of reckoning. The sunan (supererogatory prayers) of the five daily prayers vary in emphasis, with the most emphasized being the regular rawatib prayers that the Prophet, peace and blessings be upon him, consistently observed. These are ten rak'ahs, the most emphasized of which are the two rak'ahs of Fajr.