Well technically its sensitivity but the difference is hard to explain so efficiency will do. Which one sounds better is impossible to say. Pretty obviously there are great examples, as well as examples that suck, of every design. For every guy who swears by electrostatics there's one in love with horns, for every port lover there's a sealed supporter.
In terms of amps though its still hard to say its at least a little more clear. Speakers with low sensitivity are gonna be a lot harder to find an amp to make them sound good. Tube or SS.
Problem being, its hard enough to make even just one watt sound good. Then if you want louder, which you do, well then both power and volume (dB) are log scale. What that means is to play just 3dB louder, which does not sound like much, requires twice the power. 10 dB requires ten times the power.
So a speaker with only 86 dB sensitivity, that on paper looks not hugely different than 92dB or even 96dB, in reality is gonna need four to ten times the power.
In practice you go with what sounds good. Regardless of how its made. But no matter how much you might fall in love with one you will be well advised to stare it down real good if its sensitivity is below 90. People do, it can be done, but the 87 you mentioned will need nearly ten times the power of your 95 example. And good luck with that. Because you will need it.
