There are a lot opinions on instrumentation.
Primary things to consider:
Isotopes of concern.
Durability.
Environmental influences.
Complexity of operation.
Calibration support equipment.
Cost of repair components.
I'd suggest contacting the instrument sales representatives and request one of your final selections on a trial bases. They will usually ship, or show up with one, when they hear the word SALE!
As far as the E-600, I like it, but it's not built for power plants use! One meter and a dozen smart detectors! Now you have to ask yourself, did the E-600 over respond, or did the other under respond?
Hope this helps, RG!