Freeza is quite possibly my favourite anime villain/antagonist, even when compared to those outside the Dragon Ball series, whereas conversely, I've never been particularly keen on Cell, so it's undoubtably the former for me.
Similarly, the Namek arc and Goku's battle with Freeza is probably my favourite. Aside from Goku's first encounter with Vegeta, it was the first major battle in DBZ, with the first appearance of the Super Saiyan. It was just an amazing fight, especially with the whole planet crumbling around them. The subsequent arcs that followed were rather repetitive and didn't match up to the tenacity of the Namek one, in my opinion.