Dragonball Z is an anime based on the second half of the manga, Dragon Ball, written and illustrated by visionary Mangaka Akira Toriyama. Basically every single adventure/action manga after the release of the popular series is formulated after Toriyama's work. The reason DBZ is so popular is not because of its deep story or strong visuals, but because of its great and fun characters, sense of adventure and as always the intense fight scenes.
I think that was an alright summary.
To the topic at hand. I'd say my favourite character would have to be Future Trunks, followed closely by Vegeta and Teenage Gohan. The scene where Trunks meets Frieza and King Cold is forever burnt in my mind as the most badarse thing I've seen in that series.