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.

 

Good suggestion, Dennis. These early-mid 1970's C-cases are great starters. The movement in Dennis' is the last iteration of Zenith's rotor automatic with quick-change date. Speaking to your issue of reliability, Lex4, you should know that Zenith has just brought this movement out of mothballs to power its new Port Royal line, so they seem to think it reliable enough to sell alongside their current Elite and El Primero movements. Its predecessors, 2522 through 2562 are all fine too, with improvements marking each new version. The letter suffix goes as follows in Zenith Speak: C= calendar, meaning date complication, and P=power, meaning rotor. 28,800bph begins with the 2562.

And over at Zenith, high-beat starts at 36000bph!

Here's a gold plated C-case in superb condition that unfortunately the seller doesn't seem to want to ship out of Germany (althogh you could always ask) just as a ferinstance.
http://www.ebay.com/itm/181033692506?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649Purchases made through these links may earn this site a commission from the eBay Partner Network

...and another from my collection that I picked up for under $400 about a year ago

 

You would think there would be, but Zenith catalogs are very few and far between. Zenith seems never to have invested much in marketing, and after poking around vintage Zeniths for a while I get the sense that company culture at Zenith was that if they simply took care of building a better mousetrap, the world would beat a path to their door. As exhibit #1, see how Heuer-Hamilton-Breitling-Buren cleaned Zenith's clock in the automatic chronograph department. Zenith came up with a much thinner, integrated (rather than modular) chronograph with running seconds and date (and a year later day of the week and month). Meanwhile, Heuer marketed a big fat inefficient modular movement with no running seconds that it had to take back to the workshop for revisions almost immediately, but touted itself loudly, racked up motorsports sponsorships and ran away from Zenith in the sales race.

Ahem...I seem to have wandered. In response to your question, your best resource is the interwebs. Part of the fun of Zenith collecting is doing the detective work. Of course, we'll be happy to answer a question or two here and there.