The main differences are size, welsummers are more like a plymouth rock in type, leghorns are small and leghorn looking. The earlobe color, welsummers have red earlobes, leghorns have white. The egg color is a big difference also. If you to feathersite and compare pics, the differences are huge. Brown leghorns are really common and lay lots of white eggs. Welsummers are not so common and lay not as many dark brown eggs.