*They both were powerful ruler n brave warriors who never accepted defeat,they were well known for fighting for their ppl n taking their empires further
*The reason for both their downfalls was their love in someway...raavan was told not to marry mandodri as it wud cause his downfall n prithvi began neglecting his duties after marrying sanyogita
*Both their dear ones betrayed them in their final battle-vibhishan betrayed raavan n joined Ram n Maharaj Jaichand(sanyogita's father) joined Mohammed Ghori and went against prithvi
*Both were admired by most women who came in their lives for example jwala came in prithvi life n sacrifed herself for him coz she loved him, geetanjali also admired prithvi, though she was a spy she trusted prithvi completely,sanyogita fell in love with him to as time passed and similarly with raavan Kanika died for him coz she had taken a liking to him,the other woman who tried killing mandodri on her wedding day who raavan eventually bought to mandodri too loved raavan and was willing to kill to obbtain him and mandodri also fell in love with raavan
the few big differences-
*Prithvi didn't turn evil like raavan did
*Prithvi didn't want immortality he just wanted to be a good king n have lots of kingdom
*Prithvi always listened to sanyogita n raavan didn't in the end after abducting sita