According to me....
Season 1: The One Where Rachel Finds Out: Very exciting, since we all want the R&R to work out..
Season 2: The One with the Prom Video: Brilliant storyline, fat Monica, Ross with the interesting hair, Rachel with the nose...Very funny and sometimes "touching"
Season 3: The One Where Ross and Rachel Take a Break: I find these eppys (the ones before and after) very emotional, exciting and funny.
Season 4: The One with Ross' Wedding: Greatest finale ever :)
Season 5: The One where Everybody Finds Out: Greatest Friends Episode ever.
Season 6: The One where Ross Got High: One of the greatest storylines ever. Chandler's dialogues with Monica's mother make me jump out of the couch :)
Season 7: The One with the truth about London: Funniest Friends moment -- Ross' model flies over the stairs, Rachel thinks it is Ross...Hardest I laughed in my life.. OR The One Where Rosita Dies is also equally great.
Season 8 (so far): The One with Rachel's Date or The One where Joey Dates Rachel
Let's hear about yours......!