I think Saurfang
he is more experienced, more clever, while Garrosh was hotheaded and stubborn
strangely, if you follow Garrosh from Wotlk to Mop, almost everyone beats him one way or another
Sylvanas outsmarts him (he wants Gilneas conquered and Forsaken used as fodde, but sylvanas gets Val'kyr, conquers for some time msot of Gilneas and avoids wiping out forsaken), Vol'Jin at first almsot leaves horde, than survives assassination attempt and overthrows him with the help of rest of the Horde and Alliance
Thrall vs Garrosh was strange one, it was between draw and Garrosh having upper hand (looking at preWOTLK event or comic side), also in the end Thrall defeated him, but used magics, before that, in SOO Thrall tried using elemental magic, but garrosh had already take elemental powesrs using Dark shamans.
so Cairne was far strogner and more cunnignt han Garrrosh, during makgora Cairne hs upper hand, untill garrosh';s poisoned weapon immobilises him
Baine has tos ave Garorsh's ass from quillboar
in Blank Scroll, even Galllywix manages to fight Garrosh using his machine, but dies by accidental bullet
Varian totally fukes up Garrosh each time they meet in fight, in wolfheart, Varian manages disarm him also he is under goldrins blessing somehow
even Anduin manages destroy bell using mallet of harmony and ruin Garrosh's plans
I even felt sorry for him