Re:
My tuppence. I own 26 ,27.5, 29, 29+ and 26 fat. 26 is purely retro and the modern bikes that I had that were 26 were on the whole pretty good at the time and I had no complaints. Until I started riding 29. The 29 does roll better, you will carry more speed and it will get you out of trouble too. In my opinion us that are a bit longer in the tooth and are no longer as fast or accurate would be well served by the benefits of the big wheel. I have followed the emergence of 29 and the negative opinions are nothing new, if you could read back on other forums 5/10 years ago you'd be reading the same thing. Only now most people are more accepting of them and indeed believe the benefits to actually be true. If it is indeed marketing then it is probably the most successful brainwashing in history
As for 27.5 well I have less evidence, the bike I have the wheel size is not the biggest factor, suspension and geometry play a bigger part here.
29+ , the bike is rigid and the big tyres provide hassle free comfort and again roll very well. I've used this for the Strathpuffer race where again it kept me out of trouble and in relative comfort without any suspension. Great for this type of thing , endurance events.
Fat bike is great again, very forgiving and it is indeed harder to pedal but unless you are racing (though I have also used this for the puffer) it is wonderful. Allows you to keep your head up and appreciate the countryside rather than focusing on the line you have to take. It's been said that fat bike reminds people of a big BMX and they really can be this much fun.
At the end of the day though a bikes a bike fur aw that. Two wheels, pedals and wotnot. Only now you have the
choice to buy whatever you want. And remember it is up to you, you don't need to buy into it but I do think that you should at least try some of them. Not everyone is merely trying to justify there purchases or have had the wool pulled over there eyes by the evil bike industry.