When I was looking for a pair of speakers for my Nord Piano 2 a couple of years ago I had the opportunity to test both the QSC K10 and the Yamaha DXR10 side by side in the store while playing the Nord Piano sounds. I sincerely hoped that the Yamahas would be the better ones (I found them aesthetically more pleasing and they were cheaper

). However, I ended with a pair of QSC K10s - a decision which I never regretted - and I had a lot of live gigs since then.
My personal reason: I found the Yamahas very muddy in the mid-range and a bit harsh in the upper end. The QSCs were far more balanced in the whole range.
Edit: When playing mono I am using the right channel as well for the same reason: In a band context I need the upper end more than the lower end which is already covered by Bass and Drums.