For 14" the best tire is the Kumho Radial 857.
For 15" I will probably use a load E st tire, and change every 3 years.
For 16" definitely a LT tire load E.
I am going through this right now, I have a single axle trailer with 15" wheels, but it is a 5000 lb. axle with 6 lugs. I have the option of purchasing cheap 16" rims and going with LT E tires, or I can step up from a load D to a load E ST trailer tire, and still have plenty of reserve. I have Trailer King bombs on there now, that have sat on a lot in Phoenix for nearly a year before I bought it.
Cost is not much more, unless I buy Michelins.
Gman