I've never fried anything in tallow, and while I keep good lard (and bacon fat) for confit, I never fry with it. However, I do fry things in duck fat, and it makes an enormous difference, both in flavor and mouthfeel.

The "best" french fries are, it's said, fried in horse fat (I first read than in Steingarten, a dubious source, but have heard it backed up repeatedly). If you Google, there's an article with someone actually tracking down horse fat and frying frites in it.