I usually used chicken oil in frying. which would you prefer in cooking, the chicken fats or the vegetable oil?

Vegetable: Always vegetable oil. There is no reason to ever use animal fats for cooking. If you like the taste, change your taste. Even with veg oil, you should use it very sparingly and frugally.

Avoid Vegetable Oils: Cooking with vegetable oils creates heat-induced damage called oxidation. As oil is heated and mixed with oxygen, it goes rancid. Rancid oil should NOT be consumed—it leads to a variety of health problems. Traditional fats, like chicken fat, consist of saturated fats which maintain their integrity when heated and do not become oxidized during the cooking process as long s the heat is kept below the smokepoint.