Nikonos.
Best inexpensive underwater camera ever. The original was a Cousteau prototype, hence the name Calypso, before it became Nikonos.
My first was a new 1965 model. My second was free the next year when I found a Nikonos that someone had dropped or lost while diving. I took it into a camera shop, had it serviced, and it still worked fine. Generally, they don't leak and they don't fog.
Reliable history, simple maintenance, different lenses, flash, the whole package.