Winter Clothing

Was just wondering, what is peoples opinion on this.

Is it better to wear multi-layers (ie thermal base layers then your normal gear, then fleece, jacket, waterproofs etc) or to invest in some really good quality Jacket/overtrousers, or winter suit purposely designed for keeping you warm, and skip all the under garments.

i wear a pair of extra socks and sometimes I wear clean pants too just in case i get run over by an ambulance.