I had my choice narrowed down to a 550 Gator or Polaris 400/500 Ranger because at 56" they were the next narrowest side-by-side after my Mule 610 that fit my needs of a nice bed, and bench seat. I did a brief test ride on the Gator and 500 efi Ranger. They both have similar ground clearance and travel with their independent suspensions, along with similar load and towing capacity. I actually feel the Gator's double wishbone front suspension should be a bit more stout than the Rangers. But then again I've never heard of Rangers having any problems with their suspensions.
The Gator I rode was a little cold natured to start but after a brief warm-up the choke could be pushed off. It had some rattles emanating from the bed area. The bed snaps down securely, but it's not held down tight which allows it to vibrate. It might not with a load in it. It rode well (much better than my old Mule) and accelerated well off the line but kind of ran out of power and flattened out, they say around 27 mph. It felt like it had just a bit more power and speed than my 13.5 hp Mule but the engine was also a little noisier and "buzzier". The Gator has a 2 cylinder 16hp Briggs and Stratton engine. I can't recall if it's liquid cooled or not. Compared to my Mule it had a much nicer suspension and more ground clearance, but barely any faster.
The Ranger 500 with its fuel injection started on the first try then settled into a nice idle. (The 400 is carbureted but I didn't try it. They say it runs about the same as the 500) With just partial throttle the Ranger felt quicker off the line and it took the bumps at least as well as the Gator. The steering is great being fairly quick yet seemed effortless, almost like power steering but it isn't. A little more throttle and I notice I'm going 30 mph on the standard speedometer (none on the Gator) and the engine is smooth. Then I floor it and it really takes off but around 40 MPH I let off. (It is a brand new machine after all) The reason it runs so much better than the Gator is it's liquid cooled, counterbalanced, single cylinder engine makes 32 HP. I later find that Polaris has been using this engine for years and it has a bullet proof reputation.
I think I would have been OK with the Gator 550 but after riding both I went with the Ranger 500 EFI. In the woods my Mule was fine but there were too many other times where it was simply way too slow and the Gator wouldn't have been much of an improvement in that regard. The best value is probably the 400 Ranger. It's engine is actually around 450cc and makes 29 hp, and the "400" is $1,000 less. (msrp $8,300 vs $9,300). Compared to the 500, the 400 is carbureted and doesn't have the speedo and tach also. I think the Gator was priced to me at $8,300 also after the JD dealer added freight and "prep".
The reason I spent the extra $1K for the 500 wasn't the extra 3 hp, but mostly for fuel injection. I believe it'll make it easier to start and idle to warm up, especially in the winter. FI tends to be less affected with ethanol. I'm also thinking of taking it to Colorado and Utah and at those elevations it should be a big improvement over a carburetor. The digital speedometer on the 500 is nice to have and the tach will be useful to check idle speed.