I always love these "I heard" things, because the source of the "I heard" is probably not even legitimate. Thing is, you can find a negative review on virtually anything on the internet, and if you listened to them all, you would never buy anything.
Always take any review or "I heard" with skepticism.
Given that, here is my opinion on your question.
While it is generally not that clear in most camera formats which brand is "best", I think the undisputed best brand of mirrorless cameras are the Sony NEX series. They are way far ahead of everyone else with the DSLR sized sensors and other features.
I think Nikon missed the boat with the smaller-sensor Nikon 1, and especially with Canon getting ready to release their APS sized sensor mirrorless camera, one wonders if Nikon has one in the works as well; which does not bode well for the Nikon 1 platform (unless of course, Nikon intends to make the Nikon the new standard for compact cameras).
However, while all of this may be true - the problem with "the best" this or that is that in 6 months, these things may no longer be true - thanks to Moores Law and the unpredictable nature of marketing.