Part of my username is actually a Dragonball reference.
I can't say that DBZ is the 'best manganime', but it certainly deserves legendary status among anime. It is, perhaps, the most influential product among anime/manga creators. I've read several testimonials from Japanese artists (particularly the creators of Naruto and Bleach) that said they wanted to make manga after seeing Dragonball.
It's a manga/show that people literally grew up with, starting in 1984 and going on until 1996 (in Japan, the end of DBZ). It's especially interesting to see Toriyama's art style become more refined over the years.
It's impossible to imagine where manga or anime would be today had it not been for DB/Z. So much of what has been produced since then has been inspired by it, and it was one of the break-through shows that increased the awareness of anime in the west.
It definitely has its low points, but when it's good it's good. I fully intend on collecting the entire DB/Z series on DVD over a period of time, this is one of the shows I want to show my kids.