Baking Soda
Which dissolves better in water: salt or baking soda?
Baking soda
Salt 359 grams/litre
Sodium bicarbonate 236 grams/litre at boiling point (when it will decompose into sodium carbonate and carbon dioxide anyway)
So, salt it is!
Baking soda becoz it is very fine but if you have a salt of good quality then it will dissolve completely too!:)