Stiff springs give a stiff ride when the truck is empty. It gives you a safer, more controllable vehicle with a load on it. Softer springs will ride better, give better compliance over rough surfaces, and make it a real pig with any kind of load in it.
It also depends on what you mean by "smoother ride". Yes, softer springs will make it less bouncy over trail bumps and speed bumps. But, I consider a soft ride to be "bad". I am used to firm suspensions on road. I don't go off road. If I crank in some steering input going into a turn and the vehicle wallows and leans and the tires scrub I can't stand it. I'd rather have a harsher ride and a vehicle that will turn on pavement than a soft ride.
Adjustable suspensions are the best thing. I don't know if they make a readily adjustable suspension system for Tacos. Motorcycles have them for a reason, the same bike has to be made to accommodate a 150# rider, and a 200# rider with a 150# passenger plus some overnight bag etc. The only way to cover that kind of range is with an adjustable suspension. Nearly all commercial trucks, even school buses, have self adjusting suspensions. The air bags you see on them, the black marshmallow looking things you can see when behind them at a traffic light, use a ride height valve to regulate the air pressure in them. When my work truck is empty, those bags have about 10 psi in them, when it's loaded, they are up around 70 psi.
One thing you can regulate is tire pressure. I run my street truck with whatever size tires come on the '15 Pre-Runner at 40 psi. It rides harder, but it turns in better with less drama. You can do the opposite by lowering the pressure. I don't know what kind of psi guys run off-road, probably around 20, but that would help. It will be a real pig on road and maybe even lead to blow-outs on the highway, so you can just air them up for on road use.
