Egg is ideal protein because it has –
Egg is ideal protein because it has high biological efficiency and NPU :

NPU for egg : 100    Fish : 77    Wheat : 51
NPU for meat : 80   Rice : 65    Pulses : 45-50
NPU for milk : 75    Soyabean : 55
High cholesterol
High protein per 100 gm
High biological efficiency and NPU
No limiting amino acid