I don't think it's quite practical to give a "one and only, clear winner" when it comes to Seiko ... but I'll give an example here that I consider a prime candidate for a "top 10" list covering the entire history of Seiko WRIST watches.
On another forum a question was asked a few years ago regarding which is the longest running model name. the J-LC Reverso was suggested as the "winner" since it was started in the 1930s (I think) and is still made today.
I answered that there was one other that could qualify even better, the Seiko Laurel.
Now the problem with the Laurel is that it hasn't been made continuously by Seiko through all the years of it's history, there were some lapses, years when no Laurel models were made. So, depending on how the question is actually phrased, Laurel may NOT qualify.
BUT ... in any case, here is "The Laurel" as I know it:
Remember that (originally), the "Laurel" was a brand (or "badge"?) of the Hattori Co. while "Seiko" and "Seikosha" were separate brands that were introduced much later than "Laurel". Ultimately, the main brand of Hattori Co. became "Seiko" with various "families" or "lines" of watches subordinate to it.The First: 1913
This was the first model wristwatch from Hattori. They were housed in a small 26.2mm diameter "double case" and were meant for both men and women (as a small pocket watch when removed from the band and outer case. They came in a variety of styles. The crown was at 3 o'clock requiring some adaptation of the A. Schild 7 jewel movement. The dials were porcelain (and likely NOT made by Hattori), and the case silver (0.900), with nickel on the back side of the outer hinge case (in some models). Genuine cases have the "SKS" mark inside the outline of a Japanese-style folding fan.
The main problem for the collector, according to one source, is determining which are legitimate dials & cases on the used specimens now sold!
It is also believed that this is the first Seikosha product "that contained components manufactured entirely in-house". I assume this to mean, all movement parts as well as the casing parts. It is however, interesting to note that a Kelek [Swiss company that was taken over by Breitling appx 1997] related website indicated that the Japanese market was important "early on" and even through World War II (WWII). It specifically mentioned that they had a "deal with Seiko predecessor Hattori"; Kelek sold movements to other firms as well as made watches under it's own label. This fact may imply that even if the Laurel were made completely "in house", that Swiss imports did continue to play a role in Hattori/Seikosha/Seiko products throughout a significant part of the 1st 1/2 of the 20th century despite Hattori's drive to do more and more in-house as time went on.
2. Laurel ca. 1948
The above picture from "Domestic Watch Series, 12; Pre-War/Post-War Edition," by Yoshio Nagao and Toshiki Mori. (Tombow Publishers, Osaka, 2002).
3. ca. late 1950s -> 1960s
According to one source, the Laurel was revived in 1958 after production of earlier Laurel models was ended in the early 1940s. However, this contradicts the attribution to 1948 as the production date of the model preceeding this entry (above):
Model 14025 ca. 1960 shown below
4. Laurel - Alpinist
The 1st model of "Alpinist" was introduced underneath the Laurel "family" in the early 1960s. Later models of "Alpinist" were then moved to the Champion "family".
There are, of course, more modern models of Laurel made by "Seiko" (as the corporate name is today, no longer "Hattori") but I will not cover them as they are not my area of "expertise".