I use a couple of cheap analogue ones from a few different brands. As long as you know how accurate your hygrometer is, it doesn't really matter. A simple salt test will give you your accuracy, and you just adjust from there. A benefit with the digital hygro/ thermo combinations is that you get multiple environmental factors being measured with one device. The humidity is going to vary in the cage anyway (being lowest right over the hotspot), so you may want to use a few in various locations in the cage. What type of enclosure is it?