The one and only acoustic instrument?

Piano offers more data for making an informed, rational decision. Guitar resonates more personally for me. So, if my left brain is running this show....

mapman

that is the coolest chart
thanks for sharing!

it would be wonderful if you touch a spot and it give the tone for that instrument

That chart helps me understand why my 2-way speakers that cross over at ~ 7khz sound (blue zone on chart) so coherent and right compared to many that cross over in the yellow and green regions. That and them being omnis make for an effective combination of fundamental design advantages.

Piano, which covers a very large frequency range and has tremendous dynamics as well. A piano playing a variety of music can show you the strengths and weaknesses of a speaker system better than any other instrument, IMHO. Plus, if you know the make of piano in the recording and have heard one, it's easy to see how well a system can reproduce its timbre. My suggested recording for testing a system is the Reference Recordings "Nojima Plays Liszt", which along with being a superb performance can certainly give any system a good workout.

The most colorful sounded instrument for me is the guitar. It might(not trying to start anything by this)be like systems. The guitar is the one instrument I can almost never tire of. For me it is not even close with any other instrument.