Which type of oil/fat should I use for deep frying?
For the very best tasting fries, onion rings and battered fish are fried in fat made from rendered beef fat. When I was a cook we rendered down a thousand pounds of beef fat a week, it took days to do. But it made the very best tasting savory deep fried foods. The burning temperature is lowish, so food needs to be cooked at 325 and changed more often. It's not good for things like doughnuts. 

I'm not a fan of Canola, I find it often has a taste which I don't like. I don't use peanut mostly due to habit, too many people I've run into with allergies. I can't find rendered beef fat and I'm not going to render it at home.

At home I use a mixture of Sunflower and lard, about 1 part to 3 parts. The sunflower oil makes it easier to handle when filtering through a very fine mesh sieve (more liquid at a lower temperature) after use, then I put it in an old olive oil can which I refrigerate between uses. I leave out overnight before I use it then warm in hot water to pour it out. I don't usually use more then once a month. The more crumbs and batter bits you filter out the longer the fat will remain good. So filter, and don't pour the last bit into the can.

Refrigerated the oil mix doesn't go bad before it becomes no good to use. I get well over a years use. I love sunflower oil, it has almost no taste at all and a high smoke temp. It is pricey.