After living with the reference line for about a year I am still extremely happy with the sound for our Sonos whole house audio setup. The thing that bugs me a bit about them is that visually they stick out a bit since the edge doesn't go totally flush to the ceiling. In hindsight I probably should have gone with a pair of 6.5" rather than 8 in the master bedroom, it's a bit overkill.
As for the other speaker options, I stand by my original mini review, Micca 8" was my favorite and 8" Monopricee was my least favorite. Honesty, for background whole house audio use, I think they would all work fine. I know lots of folks are very happy with the Monoprice speakers and same with the Polks. Once you turn up the volume a bit, I found the Micca Reference line really set itself apart from the rest.