Personally I find labeling a series as "better" than another is an utter waste of time because it's all a matter of opinion and no individual is good or intellectual enough to create legitimate standards for quality in a sense that everyone can agree with.
Never watched Rurouni Kenshin, but I've heard it was a good series. That said, I have heard that the manga was LEAGUES better than the anime.
As for DBZ, I honestly don't think it's that great. I have fond memories of it as a child and there's some nostalgia, but as a story it's not particularly strong. The plot is extremely repetitive, character development is minimal and restricted to a very small set of characters, and there's little that makes it stand out qualitywise as a masterpiece among Shounens. If anything I'd say Dragon Ball part 1 should be recognized because of its martial arts nods, adventure elements, and much better humor.
To put it simply, you don't have the right to say that only one anime is "better than" DBZ because I heavily doubt you have seen all other anime in the world. In fact I know I've seen very little anime in the grand scheme of things, especially when I compare my own list to that of many others, and I can STILL say that DBZ would not even be in my top 50 anime. Don't even get me started on manga.
