There's a lot of difference in those three tires.
The radials obviously have radial constrction. That means the plies and belts run around the cidcumference of the tire. This makes for a tire that rolls easier on a flat surface. Because of their construction, the tread wants to flex in an even plane. Not so good for wrapping around sharp trail obstacles. Their soft sidewalls flex well and make up for some of this.
Bias tires (TSL) have their plies going accross the tread. This makes the tread quite pliable, and it can wrap around rocks and stumps quite well. They do not want to roll quite as well on flat surfaces and the sidewalls are quite stiff.
SX is a bias belted tire. This is kind of a hybrid between the bias and the radial. Basically it is a bias tire with some radial belts added to try to gain some of the flat surface rolling ability of the radial. Unfortunately, this extra construction makes for a stiffer tire, so on the trail, you need a heavier vehicle and/or less air pressure to make this tire perform well.
Most people think the sidewall treads look cool.
These tires are heavy too. A 38x12.50 TSL weighs 72lbs. A 38x12.50 TSL/SX weighs 81lbs. That's an extra 9lbs on an already heavy tire.
The biggest TSL Radial or TSL/SX you can get currently is a 38". Same thing for 16" rim size. If you want 39.5", you have to go with the regular TSL.
Tires this large will last a good bit longer than most people think. You need to make sure you are not over inflating them as this is one of the leading causes of extra wear on larger tires. Make sure the whole tread width is in contact with the road by doing the chalk test.
I run about 16psi in my 38" TSL's.
Still Poundin' "pavment" after all these years!!!