I'd prefer tandem axles too, for the reasons Dee so eloquently cited, but there ARE a couple "cons" to them too. They're more expensive - you have 4 tires, 4 bearing sets and 4 brake assemblies to periodically service and or replace. AND, you have to be very careful to get the trailer as level as you can while towing. Otherwise, if the nose is high, the rear axle on the trailer is carrying more weight and the reverse is true if the nose is low. Since each axle/wheel combination has a fairly low individual weight carrying capacity, it would be relatively easy to overload one of them if the trailer was not level.
A good Weight Distributing Hitch (WDH) makes leveling a trailer easy, but I've seen lots of trailers set up improperly with a WDH, usually, nose-low.
- Jack