If you want a quality 1.6 gpf toilet do not go to a “Box” hardware store! See a plumbing supplier or your local plumbing contractor. These people know which is best.
However there is often, in older houses or in houses not plumbed properly, a lack of proper venting. A 1.6 gpf toilet will perform miserably under these conditions. I prefer power assist toilets in this situations, i.e. Gerber Ultra Flush.
Good luck