Pandas max value index
Use argmax()idxmax() to get the index of the max value. Then you can use loc
df.loc[df['favcount'].idxmax(), 'sn']
Edit: argmax() is now deprecated, switching for idxmax()
I think you need idxmax - get index of max value of favcount and then select value in column sn by loc:
df = pd.DataFrame({'favcount':[1,2,3], 'sn':['a','b','c']})
print (df)
favcount sn
0 1 a
1 2 b
2 3 c
print (df.favcount.idxmax())
2
print (df.loc[df.favcount.idxmax()])
favcount 3
sn c
Name: 2, dtype: object
print (df.loc[df.favcount.idxmax(), 'sn'])
c