What is the difference between spring axles and torsion axles?

If everything else was equal, for a 3 horse BP, would you go for 3500# Spring Axles w/Equa-Flex Trail Air (whatever "trail air" is) or torsion axles?  Explain your choice, please. ;)

How about 5200# spring axle vs. 5200# torsion axle?

Is is true that torsion=rubber and spring=metal?

Is it true that torsion axles are quieter/smoother but don't last as long as spring axles?

Torsion axles are a steel tube with a rubber interior. The torsion bar lays in center of that rubber. As the arm moves up and down in travel, the Torsion bar Twist. The rubber provides the resistence agains the twisting of the bar. So the rubber does not support any weight, but rather increases the resistance to twisting

Springs are similar to the leaf spring you see on most pickup trucks.  The axle is steel and is connected to the springs.

You can build a trailer lower to the ground with Torsion bars than with springs,  Almost all new horse trailers come with Torsion axles. They allow the trailer to not be so high in the air. They are just more compact and take less space.

I don't know about life expectancy. Mine are 6 years old and no problems.  Samw ith noise, I don't have the answer, Somebody else will have to address that.

3500 vs 5200 axles are dependant on how heavy your trailer is. A smaller trailer will ride just fine on a pair of 3500lb axles for a total load of 7000lbs.  The same trailer with dual 5200 axles would be rated for 10,400 and that may provide more bounce than you really need.