Based on my unprofessional testing, if you want to ride recreationally, cruise the trails at a diesel pace vs. sprint without getting beat up, then a plus sized tire may be for you. If you plan on blitzing descents and technical sections, hitting jumps and drops, cornering at mach-stupid, then plus is probably not the best choice. I think that tire size depends on how you plan on riding more than what is appropriate for the trails around here.
My experience is wildly different than this. The fastest time i've recorded both up and down have been on 27 x 2.8" tires. This is a great time to be alive. Literally more options than you could ever have a chance to ride and experience. I'll add the caveat that carbon wheels really complete the 27+ experience and that without them it's a lesser animal. I rode 29ers for ten years and much of it on a longer travel 29er. Just a few rides in California on 27+ and I was convinced to give up the much loved 29er wheel.
That being said, we may watch as the lines blur and 27 x 2.6" becomes more of a the standard fare. I have a good friend who works at Schwalbe and he says all the OEMs are betting heavily on 2.6" for 2018.
What we are seeing is:
-if you are racing xc = 29 x 2.2 - 2.3ish
-Just playing and having fun (mostly w/o a number on your bike) 27x 2.8" - 3.0"
-Drive a hummer or Jeep or just love attention 26 x 4"-5"
-love to jump more than pedal 27 x 2.3" - 2.5"
-eyeing the bike packing thing 29 x 3.0
This is of course a wild generalization and results may vary.
I can say that at the demo events I've worked, the biggest smiles and positive responses come from 27x2.8".
All this means is that you should demo a bunch of stuff and make up your own mind as to what you love, like or hate.
