Lol! I use McDougalls; despite what the label says, I generally sift flour (unless I'm making my Victoria sponge mix, and then I don't). That way, you can always remove any lumps, check there are no weevils in your flour and ensure you have added as much air to the mix as possible.
Always make sure your flour is stored in a jar or put in a zip lock bag in the flour packaging, that way no moisture can get into it.
I have bought the self-raising version for supreme sponges because I wanted to see what it was like. (I'll let you know when I've used it). I suppose it's the same principle as granulated vs caster sugar. Caster sugar is lighter and finer grain, so it gives you lighter bakes, but half the time, I use granulated because...