I don't know too much about RealTemp...I do have CoreTemp and it seems pretty accurate, considering I'm using a MacBook. Idle is always between 54 and 60.
An intel E5200 at 2.5Ghz with a Zalman CNPS9500. I always used coretemp however I was a little curious as to why my CPU temp was quite high. I just looked in the BIOS and it seems to be hanging around 31-33 celcius so I may go by what real temp tells me.
I say whatever floats your boat. There's a lot of debate between bios temperature and core temp etc etc. Core temp seems to work for me, though I don't have bios, so I can't check what it says, haha.