Thanks in large to Cartoon Network and Toonami, many westerners grew up watching Dragon Ball Z. As well as serving as a fantastic gateway anime, the series' success also encouraged viewers to check out its predecessor, Dragon Ball, with the general consensus at the time being that Z was the better of the two due to its high-octane fight sequences and stronger visuals.
As time has gone on though, and with subsequent watch-throughs, a lot of Dragon Ball fans are now starting to change their minds, with many now believing that Dragon Ball is better than Dragon Ball Z. Of course, this kind of thing is highly subjective, so not everyone is going to agree, but there are a few things that the original Dragon Ball anime arguably does much better than DBZ.
Martial Arts Mastery
Though it featured some supernatural elements right from the get-go, Dragon Ball started life with a much heavier focus on martial arts than its successor. A lot of the series' earlier storylines revolve around Goku's training, with new techniques often playing an important role in his victories rather than the Saiyan simply relying on brute force or flashy transformations as he ends up doing later on.
For those with an interest in Japanese martial arts, the Dragon Ball anime will likely make for a much more satisfying watch than Dragon Ball Z. The regular World Martial Arts tournaments ensure that there's a healthy supply of well-structured one-on-one battles for viewers to sink their teeth into, while also introducing them to a large and diverse cast of secondary characters in the process.
Better Pacing
For as iconic as Goku's fight with Frieza is, many people remember it for all the wrong reasons. The five-minute countdown to Namek's destruction is perhaps chief among them and is often ridiculed due to the fact that this supposed five minutes somehow manages to span multiple 20+ minute episodes. Dragon Ball Z Kai did improve the pacing of this sequence a little, though, ultimately, this is an issue that plagues most of Dragon Ball Z in one form or another.
By comparison, fights in the original run of Dragon Ball tend to be a lot more fluid, with very little filler used to pad out the series. Of course, that's not to say that it doesn't still have issues from time to time, but, for the most part, Dragon Ball keeps things moving at a much healthier pace than DBZ, ensuring that viewers spend a lot more time staring at their screens than they do glancing down at their watches.
A Focus on Adventure
Fighting may have always played a central role in Dragon Ball, but the original series made a point of exploring a few additional themes and ideas as well. A lot of episodes had a heavy focus on friendship and adventure, with these two motifs working together incredibly well and perfectly complementing the overarching martial arts narrative that really defined the series. Sadly, this all changed in the years that followed.
With the transition to Dragon Ball Z came a drastic change in ideas, with the franchise shifting to a repetitive cycle that quickly became stale. Each new saga brought with it an even more powerful enemy, with Goku and his friends then relying on new Super Saiyan transformations to eventually save the day. Granted, the series did take viewers to an alien planet at one point, but Toriyama and his team opted to focus on a stream of near-constant battles rather than explore planet Namek to its fullest.
Humor and Fun-Filled Episodes
One of the major consequences of the aforementioned shift in focus was that the tone of Dragon Ball Z was a lot more serious than it was in Dragon Ball. This, in turn, meant that there were far fewer opportunities for fun and humor in the former. To be fair, this isn't exactly a big issue when looking at Z as a standalone series, especially given its target audience, but it did create a rather blatant disconnect between it and its predecessor.
This is because humor played an important role throughout Dragon Ball, with a young Goku often getting himself into trouble due to his immature antics. It could perhaps be argued that the franchise itself aged with its viewers, with Dragon Ball being more age-appropriate for pre-teens and Z targetting a teenage demographic. Looking at both through older eyes, however, there's a certain charm to Dragon Ball that just can't be found in Dragon Ball Z.
Better Character Development
There's definitely an argument to be made that some of the humor found in early Dragon Ball episodes hasn't aged all that well, though it arguably still works due to Goku being a child. This also allows for a lot of intense character growth, with Goku forced to mature at a rather rapid pace due to the serious situations that he finds himself in. By contrast, however, DBZ Goku barely changes throughout the series and is consequently one of the shallowest shonen anime protagonists of all time.
Goku's not the only character with an interesting arc in Dragon Ball either. Both Piccolo and Chien are incredibly well-developed, gradually shifting from foe to friend over the course of the classic anime series. DBZ fans may point to Vegeta's redemption arc as an example of Z's ability to adeptly explore its characters too, but, when all's said and done, Vegeta's arc is incredibly similar to Piccolo's, just stretched out over a much longer period of time.