python pandas select rows where two columns are (not) equal

Use the complement operator ~

hsp.loc[~(hsp['Type_old'] == hsp['Type_new'])]

which gives:

   id Type_old Type_new  Len_old  Len_new
1   2      Num     Char       12       12
2   3     Char      Num       10        8

When dealing with Boolean operations, the complement operator is a handy way to invert True with False