Map display cannot be an official means to verify your LOC and Glide Slope.
You must verify the LOC with an NDB or VOR radial, and Glide Slope with a DME or LOM (or, as a last resort, an ATC radar position).
Once you have done so, I agree a MAP display is better.
There can't be an absolute truth, the important thing is to make a good valid check.
Display mode preferences depend on how your company believes you are gonna tend to make these checks: if they think you will be lulled into a false sense of security by a MAP display, they might impose you the use of EXP VOR/ILS.
I would leave the choice to the captain, but ground him if he fails to check his Glide Slope by the correct method.