It depends on what you're trying to achieve with your meal. Butter will give you the recognizable taste and helps your dough to rise. On the other hand, oil can be more beneficial for your overall health and gives you the flexibility of choosing the taste that you like the most.
While frying, you'd never want your frying fat to burn and smoke. If your recipe calls for butter frying, better use clarified butter. You also don't want to fry in the oil where the fatty acids are unstable, such as linseed oil.
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