You could use any of the three. Canola has a mild taste and I think it has the least trans fat. Shortening would probably yield the best taste (Krispy Kreme uses a partially hydrogenated shortening). Peanut would be fine and has the highest flash point of the three but is also the most expensive.
Choice in oil for deep frying is always up to debate..for doughnuts...well I think any light oil (veg, canola...etc.) But shortening is the best for fried chicken or french fries for that matter (of course duck fat would be best frech fries...but what home cook can do that? lol) Doughnuts? go with a light high temp oil!
Lard was not up to questioning...Lard is always the best way to go...if not thinking health aware...but the options were shortening vs. light oil...shortening is Crisco...not lard...lard is rendered pork fat...all things good in lard!
I don't make them anymore but, I used the dreaded Crisco!
That's what my mother used.
Remember Aunt Jenny from Spry?
The other day I read an old cookbook where after the doughnut was fried, in lard, they immediately dunked it in boiling water for a split second and then placed it on brown paper to drain. The recipe said that this procedure removes much of the grease from the doughnut and creates a superior product. Are any of you familiar with that, it was new to me.