I'm going to have to go with the traditional Vietnamese breakfast of pho, which is a bowl of noodles in a broth with beef or chicken. It's delicious and it's filling, but it's also what everyone eats in Vietnam.
Pho, hands down. I can't find it anywhere around where I live that does it the same. We do have a Vietnamese style restaurant and they do have very nice pho but it is not made the same. I can tell the difference.
I can easily say pho but I will say that bánh cuốn is more of a favorite for me when i really think about it. I can eat ramen to relieve the itch from pho but I have not been able to replace bánh cuốn.
Pho. I am obsessed with it. I am sure you can tell by my username. I eat it as much as I can every time I am in Vietnam. I can't get it anywhere else where I actually enjoy it.
Pho AND nems. I will add pork or fish caramel, fried fish (a specialty of the South), shrimps in coconut milk, H'mong black sausage (though it can often be too fatty), BBQ pork spare ribs in honey sauce, sautéed wild mushrooms, and black rice