Which is the most common type of embryo sac in angiosperms ?

Monosporic embryo sacs are more common in flowering plants. In this type, four megaspores are formed during megasporogenesis and out of four megaspores, only one is functional and the remaining three are degenerated. In functional megaspores, three generations of free nuclear mitotic divisions occur to form 8-nucleated embryo sac. Example: Polygonaceae and Piperaceae

(1) Tetrasporic embryo sacs are very rare in flowering plants. In tetrasporic embryo sac, all the four megaspores formed remain functional. During meiosis, there is no cytokinesis in meiosis I and meiosis 
II. Such embryo sacs are formed due to one generation of mitotic divisions, and all the four meiotic nuclei are functional. I Example: Adoxa, Plumbago, Penaea type 

(3) In monosporic embryo sac, there are always 3 generations of free-nuclear mitotic divisions, and not two.

(4) Bisporic embryo sacs are less common than monosporic embryo sacs. In this, after meiosis I, one of the cells of dyad is functional and the remaining one is degenerated. In the functional cell of dyad, there is free nuclear meiosis II and two generations of free nuclear mitotic divisions occur to form 8-nucleated
structure and 7-celled embryo sac after cell wall formation around the nuclei of respective poles. Example: Allium, Endymion.