Or as usual the truth lies somewhere in the middle. People who say the 6+ lags frequently are crazy. Does it lag occasionally, absolutely. My iPad Air 2 lags occasionally. The only constant lag, for me, on the 6 Plus is going from Google Music to the app switcher, that lags ALL THE TIME. Annoying, not a deal breaker.
People who say the 6 Plus is riddled with constant problems like lag or crashing have little credibility with me. I ignore them and move on. It just isn't true in my case except for an occasional hiccup. I got rid of an iPad 3 because it was horrific. The 6 Plus? Not even close.