i think the frieza saga has more feeling in it. its much more involving for all the characters...
spoiler: Vegeta dying, goku realising his saiyan ancestry, his eventual rise to the one true super saiyan, seeing his freind die in front of him. its just so much more emotional than any other saga. and of course, its where dragonball z was supposed to end. with goku freeing the universe from frieza, and dying on the planet namek
the cell saga is pretty good too actually, i liked cell as a character. he was the ultimate bad guy. but imo frieza was tougher. i mean, he managed to keep fighting after being cut in half. cell kept regenerating like a pansy.
frieza might be the fruityest bad guy, but as proven by him and kefka, fruit = badass.