My go to biscuit for a few years has been chocolate hob nob. Custard cream is my all time favourite though mate.
Into the bin with you.
Everyone knows, that custard creams, fall apart when dunked.
The true mark of a biscuit, is it`s ability to stay in one piece, when dunked.
As @anjelikaferrett says, the chocolate hobnob is the king, as it can withstand multiple dunkings. ( not when covered in butter through ).