Sailed both within six months. No difference between them except the casino . I can't remember where both had Movie Under the Stars (MUTS)
Also they might of had different specialty restaurants as well.
SS Ithaca , Volendam , Mariner of the Seas (x2) , Veendam , Coral Princess , Island Princess (x3) , Emerald Princess,Sapphire Sapphire (x3),Diamond Princess