I like quite a few of the Kanzenban covers produced. Though Toriyama's art style has declined in many areas, there are a lot of improvements, especially in colouring and tones. He's also become far more adept and detailed at drawing older characters over time, as evident with these covers of Roshi, Piccolo Daimao and Kami.
My vote has to go to the Kanzenban cover featuring SSJ Goku in his iconic pose though. Along with the pose being so iconic it's been featured in more media, both DB and non-DB (eg. Polnareff's pose during the Vanilla Ice arc of JJBA) than anything in DB other than the Kamehameha, and maybe the Goku VS Vegeta stance, the detail and proportions of Goku show an example of Toriyama's prime, with it holding even higher quality than it's depiction in the original manga.
