Tandem is nice for the oh oops issues cause by texas summers. You can always ratchet an axle up and keep doing down the road.
I judge trailer decisions based on how much weight I'm hauling. A 12' single axle will have a 3,500lb axle. Trailer itself probably weighs ~1,000lb give or take. That means your actual capacity is more like 2,500lb. Rule of thumb for trailers says load them at ~85% and you'll avoid problems (blown tires, etc). So, you're looking at 2,125 lbs realistically.
Polaris crew 800 weighs in at 1,500lbs dry. Wet weight is probably closer to 1,700 lbs. So, that means with a single-axle your now looking at 2,125 - 1,700=425 lb additional capacity. You can get away with a couple coolers, but you're not going to throw 1k lbs of feed on in addition to the Ranger. If you want to that better step up to a tandem.
I like my 12' single axle for most trips but every now and then I'll hook up the 16' tandem if it's a heavier load.
If I had a big UTV like a Ranger Crew I'd probably go with a 16'tandem. Sure is nice to be able to throw other stuff on the trailer.