If you mean «the best» (i.e. the animated series with the highest quality ever created), again, quality is a completely subjective concept that is inevitably conditioned by one's own personal bias, as objective and ubiased someone tries to be. In my view, I don't think Dragon Ball is the best animated series ever created, I've seen quite a few series that I find to be more deserving of that title, but again, that might just be my personal taste speaking. I should reiterate that quality IS NOT an objective concept. For instance, one could make an argument that the Avengers is a better movie than Citizen Kane. I personally think that's a blasphemy and laughable, but it is perfectly legitimate if someone decides to make that argument as long as it is exposed in a minimally articulate and rational way.
On the other hand, while I don't consider Dragon Ball the best anime of all time, it's also very far from being a "garbage dumb show full of plot holes, Toriyama is an hack at writing herp derp" like some «edgy» immature pseudo-elitist anime fans claim. I'm a bit of an elitist prick myself (I find popular series like Code Geass and Attack on Titan to be ridiculously overrated mediocre and generic shows) and even I can see that Dragon Ball has far more qualities than some people give it credit for. Unfortunately nowadays there's this common misconception that something needs obligatorily to be mature, gritty, complex and 2deep4u in order to have quality. It doesn't (and this is coming from a huge Evangelion fanboy btw). Elfen Lied is full of «mature» and «deep» themes and it's one of the worse animes I ever watched (I do love Lilium though). Some people mistakenly see DB's gag-y tone and the fact that it almost never takes itself seriously as a weakness when it's actually one its greatest strengths. This is the type of story Toriyama wanted to make and I much rather have it like this than having forced political and philosophical messages shoehorned into a story, when in the end the execution most of the times just ends up being shallow (looking at you Kishimoto).
Dragon Ball is easily at least in the top 3 of best long-running battle shounens ever. Rurouni Kenshin despite being published on Jump, I see it more as a historical/period action-drama rather than a traditional battle shounen, plus it has almost half the manga volumes Dragon Ball has so I don't think it's a fair comparison. Naruto actually had the potential to be better than DB if Kishimoto didn't screw everything up in Part II/Shippuden. I haven't got to see Jojo's Bizarre Adventure yet so I can't comment on that. As for HunterXHunter, I only watched the 90's series and while I enjoyed it a lot, the experience doesn't feel as «complete» as DB (I may change my mind when I find time to watch the 2011 series, but for now DB wins). Other shows like Bleach, FT or Katekyo Hitman reborn are also all vastly inferior to Dragon Ball IMO. One Piece is very possibly a better shonen series than Dragon Ball, though I can't say it with certainty since I dropped it by episode 100 something (the extremelly slow pacing combined with the insane episode count discouraged me to continue watching but I will surely give it another shot someday). With that said I definitely understand the appeal of the show and even if I only watched about a seventh of the entire series it was enough for me to fall in love with the creative richness of the world Eiichiro Oda created. "Coincidentally", One Piece is also by far the most Toriyama influenced work out of all modern shounen titles.
Dragon Ball has this peculiar effect on me (in a good way) that despite me being able to recognize all its flaws and shortcomings it still manages to be the series who I am the most passionate, addicted and fanatical about. Throughout the years I noticed - both IRL and online - that a lot of fans feel exactly the same way, we are very aware of its flaws but we still love it unconditionally. So while DB may not be the best series ever created, it definitely has something special in it that sets it apart from the rest and makes it a series on a league of its own.
(sorry for the wall, that got a bit out of hand
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