Digital only - have not seen a trustworthy analog hygrometer for less than a few hundred dollars.
Salt test is great if you're wanting to use the hygrometer to gauge an environment in the neighborhood of 75% RH. Since these are cheap, consumer-grade products (vs. something you would purchase for a laboratory or historical archive), their accuracy varies widely (+/- 5%). I'm much more curious to know how they perform in the upper 50s to mid 60s RH, since that is the environment I store my cigars in.
I learned to rely on and trust my digital hygrometers only after using them for years and comparing what they read and how the cigars smoke. When the hygrometer reads, say, 62% RH, I know my cigars are well-kept, in spite of not knowing what the actual RH is.
Eventually, you get a feel for how a particular humidor/coolerdor/wineador behaves with respect to regulating temperature and humidity. My hygrometers have been out of batteries for a few months, now, and the battery size isn't easy to find in local stores. I'm not terribly concerned because I know my humidors. I added water to my humidification beads when I realized I hadn't done so in about 6 months and a few cigars I sampled were a touch on the dry side (fantastic flavor, but burned quicker than expected).