I’ve always liked the Suunto Escape 203 for a handheld. It’s compact, light, and relatively inexpensive at $140. The fact it’s a handheld, not a wrist-mounted device, means it’s more user-friendly, with easier-to-push buttons and a bigger screen. And, it has all the stuff you’d want in an altimeter: readings to 29,500 feet (THAT oughta be high enough), altitude increments of as little as three feet, rate of ascent or descent in feet per hour or per minute, temperature, barometric pressure, and lots of other good stuff. It also has a “temperature-compensated” function, using a well-tested logarithm that takes temperature into account when calculating the altitude.
Brunton’s Sherpa, aka the Atmospheric Data Center ($159), is very similar in design, function, and general specs. It also includes an anemometer to measure wind speed, which may be handy. It’s temperature-compensated, but in general the altimeter use is a bit fussier than on the Escape, requiring frequent baseline re-sets.
Thommen’s mechanical altimeters, of course, are fondly remembered by any mountaineer who climbed before, say, 1990. Pretty accurate, but a bit temperamental聴once you start to go “wrong,” you really go wrong. And they’re expensive聴up to $300. But they’re beautiful gadgets, no question.
So, I’d go with the Escape. For what it’s worth, when I climbed Denali six years ago I wore an Avocet Vertech wristwatch altimeter ($160). It was exceedingly accurate and remains one of the better wrist-mounted altimeters.