Which is better in egg drop soup chicken stock or chicken broth?

Chicken broth and stock are pretty much the same thing. If you are having it soon after it was made it is broth. If you put it away to use as a starter in a later recipe it is stock. When making it as stock, there is a preference for cooking/boiling it longer to boil out the liquid so it is more concentrate (less liquid). That way it takes up less space in the refrigerator or freezer. Because it is more concentrate, it may be a little saltier.

Chicken soup is good on its own and is relatively saltless, unless you use koshered chicken which uses salt in the preparation process. If you need to avoid salt, you can eliminate it entirely and/or substitute other seasonings such as pepper, garlic, cumin, cardamon, etc. You can also you marketed salt substitutes that lower the sodium content by mixing regular salt with calcium chloride or other equivalents.