Yes, GOOD flannel is a thing of beauty - I love a good hearty thick flannel. NOT the thin, pilly stuff!!
Growing up, almost all of the quilts I had made by my maternal grandmother were flannel-backed, so for me it feels like that's what you're "supposed" to use. I don't always, but probably about a third or more of my quilts have had flannel backing, and a couple have flannel tops too.
Some of the best flannel I've bought has come from Connecting Threads, btw. Thick, dense, & durable. Love it.