[Corsair]

The good thing about magnetic trigger is that you're free from angle problems. The bad thing is that it must have the right depth in regard to draft of target (which can lead to misses in rough weather when the draft is always changing) and you increase chances for premature explosion. I don't use them before 1941 and only by calm seas.
Although you increase the chances for a "one shot sinking", I find it is balanced by a higher percentage of misses.