they aren't in as much demand, a few models excepted. That is because for many years modern Zenith made...er...idiosyncratic models that did not enjoy wide popularity, and because Zenith never had huge name recognition outside of Europe. The revamping of Zenith design under new (since 2009) CEO Jean-Frédéric Dufour, tapping heavily into the vintage Zenith design language, has brought new attention and prices are beginning to rise. That lag has been great for those of us who were turned on to the quality and range of vintage Zenith a few years ago. IMO, even well-known and highly sought after models like the early Primero chronographs remain good values in relation to comparable Heuers, Omegas, Longines and the like, not to mention ignored model lines like Defys, Captains and Sportos, as well as the numerous good quality nameless models Zenith produced. Only cal. 135 chronometers are probably at the 'hold' level right now - nearly everything else is at 'buy' or 'strong buy,' to use investment language. Of course, the first requirement is to enjoy yourself.
Where to start? Depends what you are interested in. Zenith has got everything - chronographs, divers, pilot watches, chronometers - it is a total watch company with almost more chronometry prizes than the next two (Longines & Omega) combined. Probably a good starter is a simple gold three hander - what the italians, who have long been crazy about Zenith, call a "stellina" ("little star") after the company logo. These can be powered by a huge variety of movements. Nearly all, both handwounds and automatics, are accurate and extremely reliable. If you don't care for the formality of gold, the "Sporto" line are three-handers usually in steel, meant for more rugged use. have a look at these and see if they tickle your fancy.