There are others on this forum with a lot more watch/altimeter expertise than myself, but I recently did a lot of searching and reading of reviews. My reading supports Craig's (implicit) suggestion: consider a Casio.
The Suunto, HighGear, and Silva Tech4O watches have persistent problems with reliability and waterproofness. Often they work fine, and there are positive reviews, but also many reports of failures and experiences like hearing from a customer service rep that, despite the "10 meter" or "30 meter" water resistance rating, "getting it wet is not recommended."
Casio seems to be the exception. There are good and bad reviews, of course, but the overall pattern suggests that Casios are far more waterproof, more reliable, and have better battery lives than any other brand of altimeter watches. Casios have crowded displays and aesthetically haven't changed much from the early 1990s (they aren't sleek like a Suunto), but they are much more likely to work than any other brand.