Should a reference speaker be neutral, or just great sounding?

A neutral speaker can still be sluggish or intransparent. ‘Great sound’ encompasses lots of things, especially the owners preferences.
A truly reference speaker in my mind should have neutrality, speed and transparency to properly sound stage, image note decay and allow for tuning through positioning. In my experience neutrality, speed and transparency are vectors on which people in comparisons tend to agree.

If you set up Magneplaners correctly, they reproduce what you send them.

If that is your idea of "reference" then so be it.

Try playing a musical instrument live--a piano, possibly, as they are somewhat difficult to record--and then play the recorded version.

If you don't hear any difference, either your ears are not trained or you have a pretty good system, I would say.

That's what Maggies do if your system is not weak in some area.

Try it and see for yourself, of course.  Don't take anyone's word for anything.

Cheers!

I’m going to make a similar comment to NoNoise, all speakers are a compromise, none are perfect. Whichever speaker sounds best to you is dependant on which compromises you’re willing to accept and how much you’re willing to pay in return (accepting that price is a compromise in itself)...

No reason to go for neutrality if you hate the sound. Rock and Techno/electronic stuff? Have at it. Whatever sounds best.
But if you're into anything acoustic or vocal, neutrality is essential.

Of course, we may disagree on the meaning of "neutral." But we will always make the best choice if the LIVE PERFORMANCE is our "reference" and not some imagined sound.

"neutral" is one of those fraught terms in audio--people are always slamming other over the head with it, claiming that this or that product sounds more "neutral."  "Neutral" does nothing because it's essentially meaningless, too open to interpretation.

Early on in my audio journey I decided the only meaningful comparison to audio gear (besides other audio gear/by contrast) was real live music, electric or acoustic, played in a known space. Audio gear that sounds "musical" (ie, like real music) wins out with me. Is this subjective? Hell, yes. But is it meaningful? Yes.

And "reference" to me connotes audio gear that takes audio reproduction even higher, with better qualities recognized & sought in audio (ie, dynamics, bass, detail/resolution, etc). I have some inexpensive, not-very-refined gear that makes music all day long, but is clearly outclassed by bigger/better gear that also makes music, albeit on a higher plane of attainment.