Whichever one is measuring the CPU die, or has a sensor closest to it is the most correct.
If you want a second opinion, use motherboard monitor. If it's available to read the CPU die, then it'll be able to pick that up. I think PC Probe is way too sensitive for my tastes.
If both temps are below 50*C, I really wouldn't worry. If it's starting to get up around 60*C, then I'd look to blow out my case real good and possibly clean off and reapply some thermal past (preferrably some Arctic Silver).