Ask most American fans of Dragonball/Z/(Ugh)GT, and they will tell you that their favorite of the three series is Dragonball Z. This probably stems from the fact that they were first introduced to Toriyama's imagination thru this series. Considering the nearly non-existent ratings for FUNimation's initial run of Dragonball, I doubt that hardly anyone was introduced to anything thru that. (Okay, my best friend was.) Antoher important factor for Dragonball Z's popularity over the other series is the "action factor". Neither of the other series can match the amount of ki beams, explosions, and simple bloodshed that Z has. But is this really a bad thing?
The constant action, from my point of view, is Z's major drawback. I enjoy seeing somebody's teeth being punched out as much as the next braindead male, but Z's CONSTANT battles irritate me a bit. In the manga, the action is just as intense, but it is not nearly as drawn out. The fact that the action goes quicker in the manga than in the anime is the very reason why the anime version of Z is so drawn out. Something that you might have learned from reading Scott McCloud's 'Understanding Comics' (If you are a comic lover, READ THIS BOOK!) is that time passes differently when it comes to film and comics. While a 14 or so page chapter of the manga can be filled easily with action, that same amount of action will not fill 18 minutes of animation. Because of this, alot of filler is added into Z. Maybe it's just me, but the fight between Goku and Kid Buu went on seemingly FOREVER in the anime. Let's not even bring up the Goku and Freeza battle...
A major reason why I prefer Dragonball over Dragonball Z is the adventure feeling of the story. I find a race to get the Dragonballs before Demon Lord Piccolo can much more interesting than watching Trunks learning to surpass the level of a Super Saiyan. (I choose not to bring up my irrational hatred of Trunks.) Speaking of the Dragonballs, that's another thing that I enjoy about Dragonball, the DRAGONBALLS are involved in the plot! While in Z this is still true, to a much lesser extent, thru the battle with Freeza, it feels as though in Z the Dragonballs really just become a plot-device for bringing back dead characters. I'm sure that some of the heroes and villains want more than that. The best way that I can describe the difference between DB and DBZ is the following-Dragonball is a comedy adventure, and Dragonball Z is action with a bit of humor in it.
Humor is the primary reason why I prefer Dragonball, it's funny. The humor is a very prevaliant element in Dragonball. The humorous atmosphere is what gave way to anthromorphic animals being involved in the plot, not to mention some of Toriyama's more interestingly-shaped buildings. Dragonball Z feels very devoid of humor at times, which is very distressing. Why keep around a monk who looks like Charlie Brown unless you try to get alot of laughs out of him?
And while we are on the subject of keeping around characters, it is the characters that I find to be the major draw, for myself, in Dragonball. DB is loaded with freakish creations such as Karin, Chaozu, Lunch, and yes, even Yajirobei was pretty interesting during his first couple of appearances. DBZ, on the other hand, pushes nearly all of these characters away to make room for...Saiyans. Characters such as Tenshinhan and Yamcha were pretty damn interesting during Dragonball, yet, in Z, they suddenly become lifeless background scenery. Toriyama's characters are basically one-note archetypes, but, to borrow some wording from John at Animenation, that's what makes them interesting. At least in Dragonball these intriguing characters, to quote ol' dirty Psaros, "had things happen to them, and they made things happen back."
While I'm still thinking of the whole Saiyan thing, I want to get something off of my chest that's been bugging me-In DB, one of the things that made Goku seem unique among the other superpowered characters was that he was always one step ahead, and had a natural fighting instinct. Is it me, or does saying that "he has those traits because his entire race was that way" make his accomplishments seem less special?
In case you cannot tell by now, I enjoy Dragonball much more than it's sequel series. Young Goku's adventures seem much more fun and interesting to me than adult Goku's battles. Of course, it could be said that the shift from adventure to fighting can be blamed on Toriyama's various editors, as you can see at Greg Werner's site in the SHENRON TIMES section. Its not to say that I don't enjoy Z, I find certain parts great (especially the more humorous aspects of the 25th Tenkaichi Budokai and the Buu saga.) and others at least suspenseful. (Gohan, Kuririn, and Bulma being trapped on Namek surrounded by several people who could easily kill them.) As for GT, well...it just sucks.