They all get the info from the same place, so once configured correctly the data displayed should be identical.
I have found that if you run more than one program at the the same time it can affect some diode readings and give strange results.
I found Everest Home the easiest to use as it auto configures and displays GPU info and is a useful complete package, but I use MBM 5 and ATI tool to display the info to an external LCD screen.