I've stuck with the same spring rates that were on the car when I first got it, as they seem to suit me. I only changed them because I needed some shorter ones on the back end.
Everyone has their own opinion/preference on spring rates.
I run a low rate spring on the back, but someone I know used to run a lightweight Nova and he insisted that 600lb rear springs were the answer. He lent them to me to try on my car, and it was truly awful in my view.