I just shop everywhere and buy what I like, and what appears to be reasonably well made. I've had good luck at F21 both with fit and better quality, and they do seem to be catering to a wider age range (I do see other women my age in the store and trying on clothes. I don't have good luck with Zara, out of all the items I've tried from them I've only kept one top and one skirt, and I had to alter the skirt.
My Gap jeans are like a Timex watch - they take a licking and keep on ticking. Although lesser quality, Old Navy Diva's fit me really well, as do other ON items. I've also had good luck with some of the brands Macy's sells, and the same goes for JCP (especially Joe Fresh).
I consider Gap, J.Crew, BR, and some of Macy's to be mid-range retailers. Whether at the high-end, mid-range, or low-end piece of the pie, I don't mid trying it all.