Which temps should I rely on?

[sprok]

I just noticed that gpu z and everest gave the same temps but were different from rivatuner and ati tool(riva and ati were the same with each other). They were 8c different so which is right?

I'm using 8800gt and 174.74.

[Brolloks]

Rivatuner and ATI Tool gives you the most accurate core GPU temp