Brand new oil is actually not as good as "older" fry oil, as slightly heat-damaged lipids are better at making physical contact with the surface of food (I believe for ionic reasons, if I recall my Dave Arnold correctly). At any rate, brand new fry oil isn't ideal for producing a brown crust as easily. That's not why I save my oil... but it's a good story to tell to myself while I'm filtering the oil and putting it back in the jar. I "backslop" old oil back into the main container, but only if it's been used to fry clean-tasting foods like potatoes. If fish or brassicas or some other such thing got fried in there, I end up disposing it.
I use high oleic sunflower oil for most of my deep frying needs. It hits the right balance between having a healthy lipid profile, high smoke point, neutral flavor, and relatively low cost. There's probably something better out there, but I haven't had the time (or the need) to explore the options in depth. Most industrial seed oils used for deep frying are a freaking nightmare on your body from a health perspective (though that's a matter for another forum). I also like to use lard and tallow from pastured pigs and cows. For different reasons, and for different applications.
The flavor of french fries made in beef tallow is superb. Apparently, if Steingarten is to be believed, a mixture of half horse fat and half beef fat tastes even better. But that beef fat french fry flavor is the core of the OG McDonald's french fry -- the Original Platonic Form of the French Fry in the American imagination. That was before the damned vegetarians and their health-nut disciples forced an industry-wide switch over from saturated animal fats to hydrogenated vegetable oils. Stupid jerks. How'd that work out for us? Want to ban trans-fats now? Guess who brought those into our dietary system, jerks!!! But I digress....
Lard also makes good french fries. Great onion rings. But it's the bee's knees for fried chicken. Chicken fried in lard? Yes. Throw in some fresh bacon fat and some rendered fatty funk from a country ham? Hell yes. Lard has a lot of monounsaturated fats compared to tallow, which makes it much more fragile from a heat stability standpoint. You can't reuse it over and over like you can with tallow. But if you're making fancy fried chicken for family supper on a Sunday afternoon? Boy howdy, get you some lard and get frying. You may well have to throw the fat away afterwards... but to think of the spent fat as "waste" is to have missed the magical work it did for you.
