I like to do it in the spring with Daylilys and Hostas... being from MN, the added cover helps the plants over winter. Some plants I cut back in the fall, like the black-eye susans and the safe and the Cone Flowers and the clematis etc etc... I guess I am a Fall AND Spring gal!!!
I best get to my pile of mulch -- we have spring, summer and mulch for our garden season!!!