The best egg layers statistically are White Leghorns (for white eggs) and Black and Red Sex Links (for brown eggs). These are the birds typically used by laying houses as they are egg laying machines, consistently churning out more than 300 eggs per hen per year. Under ideal conditions (good lighting and warm temperatures) White Leghorns are unmatched. A White Leghorn holds the laying record with 371 eggs in 365 days. However, in very cold winter temperatures, Black and Red Sex Links hold up better and will actually outlay White Leghorns under those conditions.
Black Sex Links tend to lay the largest eggs with double yolks not being uncommon. Other breeds that have a well deserved reputation for laying very large eggs are White Leghorns, Red Sex Links, and Black Minorcas.
Where egg yield is concerned bantams are generally poor layers. Even in those bantam breeds like RIR bantams that tend to lay at a good rate, their eggs are considerably smaller than their large fowl counterparts.