FWIW, I like a shell, with a 200wt fleece under it for most day's. My insulated Marker jacket I only wear when it's single digits or colder F.
I have a light weight Cloudvail that I wear when it's wet out, my yellow TNF shell has more layers and is good for most day's. If it's starting out inthe 40'sF I'll wear a wind proof fleece with my normal base layer and light weight zip T neck.
I guess the answer is...there is no simple answer. But I hope you get the idea.
FWIW, I buy all my base layers from either www.campmor.com
Great stuff, low prices, my 200wt Campmor pants are over 20 y/o still work great.