I have travelled a lot in sleeper buses a/c and non a/c both , it was very wonderful journey in sbc- bgm- sbc,
Sbc-mas-sbc,
But my first preference is one and only My favourite Trains ЁЯЪЖЁЯШНЁЯШН.
Only disadvantages of buses is road traffic ( peak hours and market areas ) and dropping points in metro cities . Etc etc......