From a pilot perspective, I like to see the least amount of clutter possible. From a mechanic's perspective, I strongly prefer instruments I can withdraw from the front of the panel. I really hate lying on my back with junk in my eyes trying to fish an instrument out of a maze of cannon plugs, wiring, and hoses and tubes.
I think the best compromise is front mounted instruments and radios, covered by a faux panel to disguise the disparity of the instruments. If this faux panel is made up in sections, rather than one big piece, so much the easier to work with.