A simple google search takes us to a result compiled by Derek Padula about the history of Dragon Ball Z in various countries. Countries in North America and others where the Funimation dub was aired first usually had Dragon Ball Z aired first.
The list of countries is not exhaustive. However, I'd like to point out "Why most of the countries (western world, and to Japan that is nearly the rest of the world) Dragon ball Z aired first.
Anime was an experimental thing in most nations outside of Japan. Dragonball was an exceptional manga and its first Anime adaptation did well in Japan. Dragon Ball creator was not happy with the first adaptation though and had a reboot in form of Z when Goku grew up. This was even more popular.
Kazuhiko Torishima, Akira Toriyama's editor for Dr. Slump and the first half of Dragon Ball, felt that the Dragon Ball anime's ratings were gradually declining because it had the same producer that worked on Dr. Slump. Torishima said this producer had this "cute and funny" image connected to Toriyama's work and was missing the more serious tone in the newer series, and therefore asked the studio to change the producer. Impressed with their work on Saint Seiya, he asked its director Kōzō Morishita and writer Takao Koyama to help "reboot" Dragon Ball, which coincided with Son Goku growing up. The new producer explained that ending the first anime and creating a new one would result in more promotional money, and the result was the start of Dragon Ball Z.
Source - Dragon Ball Z (Wikipedia)
Western media channels decided to pick up Dragonball Z as an experimental thing. It started airing in 1996, but halted after some episodes. However, when it began airing on Cartoon Network's Toonami block, it got huge boost in the popularity. Due to the success of the reruns, FUNimation began its in house dub of DBZ.
It is reasonable to assume that, due to the success of DBZ, the media houses decided to cash in on all the positive reviews and started airing Dragon Ball as well. After the success of DBZ in North America other markets also started airing DBZ and then followed by Dragon Ball.