Interesting hypothetical question.
If I was limited to just one thermometer (and I’m glad I’m not!), I’d go with a lower-priced digital Polder probe clone. It can easily be used for measuring grate temps then moved to read internal temps and its temperature limits are well within the range for low and slow cooking. The $15 clone is roughly half the price of the Polder brand so it wouldn’t be too distressing if I destroyed one through exposure to rain or just basic mishandling of it.
I have no complaints about the quality of my Taylor clone. It’s operated flawlessly for countless hours over the last three and a half years on the same battery it was shipped with.
Wireless remote thermometers are gaining in popularity, but they’re not foolproof and signals can get lost. Besides, I don’t think I want a thermometer with more technology built into it than any of the first three cars I’ve owned had.
If you’re talking about permanently mounting a thermometer on your WSM, good analog thermos start at about $20 and go up to however much you’re willing to spend. Mounting one requires drilling a hole in the dome in the desired location. The size of the hole depends on the brand of thermometer. Some will need a 3/8” hole while others require 13/16”. Another thing to look for in a thermometer is the length of the stem. Longer stems might touch the food and give false readings.
I just mounted a Brinkman thermometer in the dome about two inches up from the lip of a new WSM last night. The Brinkman has about a 2” stem so it won’t touch the food on the top grate. Because the shorter stem receives more direct heat, when the center of the top grate is at 225 (as indicated by the Taylor), the Brinkman will read 240.
For the best of both worlds, I use the Brinkman for measuring grate temp and the Taylor for the meat’s internal temp. Others get by just fine by moving their Polders to read the temp at a desired location. It’s a matter of personal choice. As with most things barbecue related, ask 10 people their thoughts on a subject and you’re likely to get at least 15 conflicting opinions.
Hope this helps. I’m sure others will jump in with their thoughts.
Ken