I switched out standard springs for progressives on my last bike (Bandit 650) as the front end was soft as puppy-dog shit and used to bounce wildly under heavy braking. It made the world of difference, front end sat a couple of inches higher and everything was firmer.
I've found that progressive springs generally provide better results on most terrains, especially dealing with changing and uneven terrain, changes in road surfaces, road conditions, pot-holes and riding with changing loads.
Upgrading to stiffer standard springs for a set load may be better if you know you're always running the same weight but if you change that, then the feel on corners and under braking will change.