iPhone 6 sales dropped from 56% down to 53% and iPhone 6 Plus sales jumped from 22% to 29%. The survey is based on 500 Apple customers. Large enough to be a trend indicator, small enough to have a significant margin of error.
I am surprised there's a jump in iPhone sales in the March–June quarter, but I'm not surprised that the 6 Plus is the one that increased.
I was one of those who laughed at the larger size and wondered who would buy such a thing. But turns out, I got it wrong. From what I understand, the Plus is better.
I still prefer the iPhone 5 generation size, but when it comes between the iPhone 6 and 6 Plus, the larger one is easier to use. The middle ground of the iPhone 6 compromises too much, and it still doesn't feel comfortable to hold (also, it's too easy to drop).
If given the choice again, hands down I'd pick the Plus.