I've been slowly compiling a personal dissertation on cooking temperatures, probes, and measuring gnat farts.....but I won't bore you with the full details of that (yet). I agree with the posts above about the cheap wired oven probes; they work well. However, as you are trying to maintain temperature, keep 2 things in mind:
1.) Those probes are designed for penetration, and the physics of measuring air is different. But, when you want general measurements, they are close enough.
2.) The probes used in these thermoâ€™s respond to temperature spike faster than temperature drop. You can test this by plopping a probe in boiling water. It will shoot up to 212 pretty quick. Pull it out and you will find that it will take much longer to return to room temperature. When you are measuring meat, this isn't an issue, because the temperature (hopefully) never goes down. Just be aware of this as you fight the intake damper to maintain temperature.
Oh, and to answer your original question, I've found that wire type exposed conductor Thermocouple wire is the most accurate way to measure cooking temp. They respond quickly and don't have a shield that conducts heat, affecting the reading. The problem is, the conductors don't hold up well to spritzing, and the thermos are expensive.
Hope this helps,