You cannot tell just by deciding for one of those. It depends on so many factors: Most of all of genotypic and ecophysiological nature. There are specific varieties that are more or less antioxidant. Could be that a variety of oregano is more than rosemary and vice versa. UV-Light, soil, plant nutrition etc. might influence the content of antioxidants as well....
most references talk about oregano being high in ranking according to the measures of antioxidant activity. However availability across the globe and the agronomy for its healthy growth would be limiting factor. It is by and large found in the eateries from eastern European and northern US sectors of the globe. However, In the Chinese and south east Asian cuisines mostly labiate find the place.