That's like asking what is the best caliber to shoot deer with, you are going to get a lot of answers. Most will be heavily biased (not surprising) because that person has no experience with anything other than what they bought.
I have a Mule PRO FXT and would recommend it to anybody. It isn't the fastest out there (still gets to 47mph), though they did just come out with a 1000cc engine that will get up to something like 60mph. It is extremely versatile, can go from a single seat with a large bed to a front and back seat and still have a decent bed in about 3 mins. Hauls a lot, pulls great, just overall a solid and very durable machine. I'd tell you to go the PRO FXT over the PRO MX. The MX isn't really a Kawi machine, doesn't have the aftermarket parts and isn't as versatile or powerful.
The new Can Ams are worth looking at as well. One of the guys on our lease bought one and aside from the wheel base being long and the cab riding lower to the ground than I would like, it's a damn solid machine. They have some pretty interesting features that I wish my mule had - such as the glove box can be removed and carried like a tool box, which would be awesome when you are out in the woods or pasture working on things. The suspension on them is badass. Bucket seats as well, which are good and bad.
I liked the John Deer SxS I had on a jobsite, solid machine. Not the Gator, had one of those one time and since it was the only thing I had, I liked it at the time because I had no choice. I also hated it. Wouldn't choose it again.
The Kubota diesel I had was slow AF, but it was designed solely as a farm/ranch work vehicle and without any sport aspect at all. More like a tank than a SxS. I had a Mule 610 for a while, good little machine but it was limited due to its size and power. The Mule 4010's are pretty popular because they have a front and back seat, but are narrow like the 610 and are more work oriented than anything else, lower powered and harder to customize due to less aftermarket available parts.
You'll have the Polaris fanboys. I have limited experience with Polaris, won't speak much other than every single person I know (except 1) that has or has had a Polaris has stated they will never buy one again because of the quality of build and the dealer service related to warranty issues. Polaris will have the most aftermarket parts because they really jumped into the game early and became the most popular due to sheer numbers and being the first that got away from the strictly work oriented SxS to a more sporty/hunting oriented model.
Kubota has a more sporty SxS that I looked at briefly, can't remember anything outstanding about it to be honest and I didn't look at it very long before moving on. And I like Kubota overall.
Stay away from diesel engines in a SxS. None of them are turbo, all of them are underpowered and all of them are slow AF.
Honda has one, no real experience with them. Seems like they had some issues on idle and running, not sure if they ever got that figured out and fixed. I remember reading a lot of complaints about them a while back.
