The best measuring loudspeaker I've heard was the Mackie HR824. It measures beautifully, even down to 1/12 octave smoothing with +/- 1.5dB throughout it's rated frequency range from 37Hz to 20kHz. It's got a beautiful dispersion pattern with the tweeter almost perfectly matching the woofer. Harmonic distortion is less than 0.5% from 100Hz to 20kHz. But yet, I can't stand listening to it.
Boy does that beg the question: What is wrong? What don't you like about the sound? What can't you stand?
Tim