I quite like the feel of linear springs personally, but it is a personal thing as YC says.
Mine were from
http://www.k-tech.uk.com/
I'd be inclined to check out what you actually need in terms of spring rate to suit your weight, for example use a site like
Racetech , click on the
Calculator link and see what they recommend.
Progressive springs by definition have variable rate through the stroke, but you want it to be in the right parish for your weight at the normal ride height. Alternatively talk to someone like Hagon direct to make sure you get what you need, not just some generic "stiffer" spring.