No stat is perfect, but surely the best available to judge the finishing ability of strikers is xG. It takes into account the difficulty of each shot, which pure shots v goals doesn't. Using all the data available at Understat.com (only league games since about 2014) Kane is streets ahead of Sterling, Ronaldo, and even Aguero.
Kane: xG = 139, Goals = 163, 17% higher than average for the same difficulty of shots
Sterling: xG = 92, Goals = 86, 7% lower than average
Ronaldo: xG = 210, Goals = 215, 2% higher than average
Aguero: xG = 126, Goals = 132, 5% higher than average
Torres: xG = 13.7, Goals = 15, 10% higher than average - very small sample size, so this one should be taken with a pinch of salt