Is saying "Marhaban" (hello/welcome) as a greeting Sunnah? Does it suffice over "Assalamu Alaikum wa Rahmatullahi wa Barakatuh"? Is its reward less? And is it permissible as a greeting even if it is not from the Sunnah?

The word "Marhaban" (welcome) and similar welcoming phrases for guests are among the noble manners and ways of honoring a guest. However, they do not suffice as a substitute for the Islamic greeting, "As-salamu alaykum" (peace be upon you). Initiating the greeting of peace is a Sunnah (prophetic tradition), and returning it is obligatory. The Prophet, peace and blessings be upon him, commanded its propagation because it is one of the outward symbols of Islam and a cause for love among Muslims, which leads to entry into Paradise. The meaning of "Marhaban" is that one has met with spaciousness and comfort. This word was used by the Prophet, peace and blessings be upon him, on several occasions to put visitors at ease.