Just a few numbers
Pochettino's record with Saints - 38% win rate
AVB's record - 55% win rate
Sherwood's record - 50% win rate
Frank dB - 60% win rate (only 33% in Europe with a -19 GD)
Benitez - England only - 59%
- Overall - 51%
Not sure it's really fair to compare by win percentages, all the other managers listed have all managed bigger/more successful clubs than Southampton so you'd generally expect the win percentage at that club to be higher anyway.