There are so many to choose from, for so cheap too.... Being for a WSM you don't have to worry about high temp cooking so the field is wide open. I've purchased expensive ThermoWorks TC's and cheap Amazon ones, they both work fine but the TW unit can take a brutal beating from both heat and moisture.
One thing I always made sure of before I purchased a TC is whether it is the isolated or grounded type. In the beginning some people were having issues when touching the TC with their hand or even touching their grill when using a grounded type TC. I haven't heard a report of this in a long time so perhaps that is a non issue now, but isolated TC's never had this problem in the first place so I stick with them.
Another thing you might look at is the size/mass of the tc. Some are little needles and others have big old probes. The thin units react fast, units with more mass react slower. Fast might seem good but in some cookers it might make the HM a bit over reactive to air flow as the blower kicks on/off. The bigger ones will react slower and therefore have a leveling effect on rapid temperature changes, while a thin probe will send the pit temp graph up and down rapidly.
So bottom line is there is no right answer, and since they are cheap you might want to try a few different styles to see what works out best for you. I think a lot of people use the type with the alligator clip and clip it to their grill grate....
