Save the world - easilly the best in my oppion, big BIG PS with all the characters (bar dead people) and a villans death by being totally vaporised, how much better can it get?
Hero's farewell - where cell is gonna blow up the world and goku intra transmisisons himself and cell to teh ki's planet, and then at teh very end of the epp cell comes back, muhahahaha evil.
goku battles 19 - goku and #19 fight, well the epp wasnt that god but he fight scene was fast, short n sweet. (by fast i mean 1 epp, and for dbz that was dam fast)
there are some other moments that are really good but i cant remember the epp names; where buu blows up earth, never saw that one comming; where frieza gets cut by his own disc, that was cool; the lead up to where frieza comes to earth, and his accident with a sword and a ssj; and of course when buu dies and goku wins at the very end.
Personally i think the best saga's for dbz in terms of plot n stuff would have to be frieza comming to earth, through androids up to cell's death. Best section of dbz, even if they did drag perfect cell and goku being unconsions for too long.
edit* looking back at everyones elses posts i feel like an idiot for writing so much, ah well.