Most people use cornstarch as a thickener because that is what has always been used. It is also widely available; HOWEVER, after Passover (the Jewish holiday) Manischewitz (man-i-chev-its) potato starch is usually widely available and on sale.
Here is a quick comparison of different starches from the website YUMMY.
Cornstarch
Cornstarch of cornflour is a fine, powdery starch that’s made from corn. It is a pure starch thickener, so compared to flour, a smaller quantity is needed to thicken the same amount of liquid. It is fast-acting too, thickening a sauce almost immediately when added to nearly boiling liquid. Asian-style dishes often use cornstarch, as sauces thickened with this starch remain clear and shiny. It is also used as a coating for fried chicken, pork, and fish.
Rice Flour
Rice flour is a type of flour derived from finely milled white or brown rice. It is gluten-free, thus it is often used as a substitute for wheat flour. Aside from being the main ingredient in noodles and native sweets, rice flour is also used for coating meats before frying.
Tapioca Starch
Extracted from the cassava root, tapioca starch is one of the purest forms of starch. It is gluten-free and is a popular thickening agent for sauces and dessert fillings. Like other root starches, it gelatinizes at relatively lower temperatures and produces sauces that are clear, shiny, and silky. It also has a less forward flavor once cooked. In Thai cuisine, water chestnuts are dredged in tapioca starch to make the classic dessert of red rubies with coconut milk. It can also be used as a coating for fried meat.
Potato Starch
Potato starch is a very refined root starch extracted from potatoes. Since it contains minimal protein or fat, sauces thickened with this starch are more translucent and glossy, with a silkier mouthfeel and a neutral flavor. It is also a good thickener for custards, puddings, and pie fillings. It is an ideal thickening agent for dishes or sauces that will be refrigerated or frozen, since it prevents liquids from separating, unlike sauces made with cornstarch.
Sweet Potato Flour
Sweet potato flour is a gluten-free root starch produced from white sweet potatoes or kamote. It is dull white in color with a stiff and somewhat coarse texture. It is commonly used as a coating for fried meats and poultry and also as a starch for gluten-free baked goods such as breads, cookies, muffins, and pancakes. It may also be used to thicken sauces and gravies.
