Pandas max value index

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

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()