I will add my 2 cents worth here as well.
I currently own a 2013 RZR 800. This was my first SXS and I got it partially because of its narrower width. I had seen the Honda Big Red in the dealers show room and thought that was the biggest, ugliest machine out there (also thought that about the Ranger and any other SXS. I have since changed my mind regarding the size of the machines.
I will lump all machines, that are belt driven, in one category . By that I mean that RZR and Ranger (both Polaris) are the same. Different uses but essentially the same engine, transmission, etc.
The vast majority of my use for a atv, of any sort, is used for work (slow speed grunt work) and off road pleasure riding. My interest in "pleasure riding" is going slow and seeing things, tuff to see much at 15 or 20 mph compared to 2 to 5 mph. This preference for slow riding demands that any of the belt driven machines be in "low gear" so as to prevent damage to the belt. That is fine but the RPM is up and the machine is noisy. My Honda Rubicon will go slow all day long without a problem if that is what one wants to do. The Rubicon has a transmission drive, 2/4 wheel, low gear, etc. It is set up for just about anything one would want to do. I would like to see the Pioneer with the same transmission setup the Rub. has. Don't know what the cost would be but what a machine that would be.
My personal comparison of the various machines on the market would be how do they work at slower speed and "brute power" demands. The RZR is a find machine but doesn't even start running smooth until about 3000 RPM (I think the 900's are a different story).
I am not sure but I think that all machines, except the Honda, are belt driven and suffer from the same problem (in my opinion) and so my choice would be the Honda Pioneer (I think).
Having said that, I will probably wait until the 2015's come out to see what changes are made before seriously considering making a change.