Are we using "current" versions of "best showings"? Because if we go by "best showings" I think Mammoth beats Rhino badly.
According to this :
http://www.comicvine.com/mammoth/29-5313/
Baran's durability has been shown to fluctuate through the years, at one point Wonder Girl and Starfire could not physically harm Baran with some of their best attacks