Different sites recommend different flours for the feeding of my established starter, so I suspect it depends on the purpose, but I can't find a definitive answer. Should I be using the flour I plan to bake with next? Will mixing and matching make a difference? Do certain types produce more activity? Better flavor?
Once my starter was established (started with organic whole wheat flour) I've been feeding it with unbleached AP flour (King Arthur) and that's worked fine. I do this simply because it's the flour I buy in large quantities to stock my pantry, and so it's generally the cheapest flour I have on hand.
If you want to "switch over" to a different flour you can always scoop out a bit of starter a couple days before you bake, and feed it with the different flour. Start with a small amount so you don't have to throw any away; just double the volume with each feeding. I don't usually bother, though.
I agree with Adam. Keep the mother alive with the 'cheapest' flour available. The yeast needs carbon hydrates. It doesn't matter much what flour you use to give it to them. Your other question, about flavor depends much more on your bread formula, bread flour, than on your mother or sourdough starter.
Whole grain rye flour is best. Because rye is better than wheat, and hole grain is better than ordinary flour. You get a better starter culture faster that way. So it is a good idea to start up with rye, even if you plan to use it for wheat bread later.