Two conflicting answers. Get a thermometer that is readable and works for you. Personally I like my oven thermometer with a probe. I waterproofed the probe with silicone tubing and tie wraps. I prefer to keep it in the mash the whole time just so I can monitor temps (I brew outdoors). The crappiest thing about thermometers is that no two read the same, and you just have to compare a couple and get an idea of which one you are going to put faith in.