I have found that realtemp, coretemp, and HWmonitor all have the same readings. The only problem with AIDA 64 that I've seen is that it will display lower temps than the others, at least in my experience. I'd rather use the ones that show a higher temp than a lower temp for safety reasons. Just run realtemp, coretemp, HWmonitor, and AIDA 64 and see which one is not like the others. I haven't found any issues at all using coretemp.