i love flannel backed quilts! but it does depend on if you want it really warm/heavy or a lighter quilt- t-shirt quilts are quite heavy on their own- adding flannel & batting doubles that- i've made both & really like the flannel best-but i live where it's cold & we like them warm & heavy- you don't tell us where you are so we have no idea if that would be a consideration or not.
if you choose flannel-follow Prisma's recommendations & buy good quality flannel so it doesn't pill when you wash it.