Brand
Georges Favre-Jacot founded Zenith in Le Locle in 1865, and the company is still there. In the early 1950s its competition caliber 135 won five Neuchâtel Observatory prizes, and in January 1969 it unveiled the El Primero, the high-beat automatic chronograph it's best known for. Zenith Radio Corporation bought the firm in 1972 and later owners gave up on mechanical chronographs, and the El Primero survived only because workshop manager Charles Vermot hid its tooling. That history makes Zenith good hunting on the used market. The A386 and the other 1969 El Primeros sit at the top, the Cairelli military chronograph close behind, and Defy, Captain and Port Royal watches get you Zenith's own movements for a lot less. Zenith made much of its own movement range, so judge a vintage one on caliber condition and dial originality.
5 references we cover.

Zenith · El Primero
Chronographref A386
$18,850–$21,025 typical ask
4 on eBay

Zenith · Defy
Diveref A3642
$1,675–$3,700 typical ask
25 on eBay

Zenith · Captain
Dressref Captain
$1,400–$2,450 typical ask
14 on eBay

Zenith · Cairelli
Chronographref Cronometro Tipo CP-2
$14,575–$18,200 typical ask
2 on eBay

Zenith · Port Royal
Dressref Port Royal (various)
$2,300–$3,325 typical ask
96 on eBay