what are your current pc specifications and your budget?
without knowing your location of purchase or personal preference, all i can recommend are the following, from cheapest to costliest:
radeon hd 7750/r7250
radeon hd 7770/r7 250x
radeon hd 7790
radeon r7 260x
geforce gtx 750ti
radeon r9 270 or 270x.
among these, radeon r7 260x, 7790 and r9 270x are of good value, unless you live in an area where crypto currency craze has driven up r9 270, 270x prices high.
gtx 750ti has been shown to have good power efficiency for performance but it's on the pricy side.