YMMV but I much prefer my 6+ I've had for a month now over the 6 I had for two.
I doubt that'll change in another month with 6+. FWIW, 6+ feels insane in stores and when you have it in real world use, I find it easier to adjust. Then again, I had a Nexus 5 and Galaxy nexus so it's not like I've never had a big screen phone before '6 series' if you will.
Sure it's not one-handable like 6, but 6 is almost not one hand able to me and I adjusted to it quick feeling like its not that much bigger than the 5 in a negative way.
the 6+ I appreciate the 1080p, I nailed the screen lottery first time though, I've seen beautiful and really meh iPhone 6 screens (mostly meh), but still that ppi and size and quality of the 5.5" screen if you get a good one, it still wows me.
Also, I use the heck out of OIS and don't want to ever be without it again, having used 6 without and 6+ with, even though they're same optics. Much easier to get sharp shots, and in certain situations, only way to.
And last but certainly not least, battery life is no slouch. Something that I could workaround with 5, but now feel way better about.
I'm a phablet fan!