The Monitor Audio would have the better reputation as having better MEASUREMENTS regarding on-axis and off-axis.
Heck, even the cheap Infinity Primus speakers had better on-axis and off-axis than the B&W 800D.
Can you see that Wide Peak around 10kHz? Doesn't matter which Generation of B&W. And these are their FLAGSHIP speakers that cost like $25K-$30K.
Here is the 700 S2. It's worse than the Diamond series. At 5kHz, it's about -8dB. Around 10-13kHz, it's about +6dB.
Sidebar 3: Measurements
www.stereophile.com
So it just depends on how you feel about speaker measurements vs reputation vs aesthetics.