I have used cotton flannels with my other cottons in scrappy quilts. There, now you've gotten all the answers! Do it if you want to!
Unless it isn't cotton, why are people saying "cottons/flannels/homespuns" as if they are different? cotton is a type of fiber and flannels and homespun are actually the type of material made out of that fiber, aren't they?
It seems like one is asking do you like "beef, roast, or ground meat"? as if one is exclusive of the other.
I've been curious about this for quite a while now....