I don’t believe that there is just one type of performance space that works best with new music. Just as there are many styles of new music composition, so are there different spaces that work best with them.
For my music, I want a reverberant space, but not too reverberant. I want a space that supports the sound—all of it—high partials as well as the fundamentals. Too much reverberation, though, and the sound becomes one big mush, with dissonances and details being absorbed by the consonances. I’ve had a few pieces performed in spaces like this, usually large, lovely churches, and have wanted to crawl under the pew during the performance, the sound bearing only a faint resemblance to what I wrote.
However, if you write monophonically for male voice (Gregorian chant), or other low-pitched, slow-moving or ambient music, it might be the perfect space. On the other hand, there are spaces that are either intentionally or unintentionally dry, where the result is the “pure” sound that is generated, with most of the upper partials disappearing before they reach your ears, with no “help” from the space (I’m obviously showing my bias here). From my experience, this type of space seems to be favored by composers of electronic music. I’ve had a few performances in spaces like these, too. I’ve always felt that I should be giving a guided tour during the performance similar to that of visiting a ruin. Instead of pointing out where something used to be, I’d be pointing out where something should have been, “this is the place where the combination tones start kicking in,” etc. In short, the ideal performance space is a matter of preference—one composer’s ideal space is (or can be) another’s nightmare.