The part of the minnow you’re using makes no difference to the fish. I do use tails occasionally, and haven’t really noticed a difference in getting bit. For example, if my Engel is on the other side of the shack and I have a pile of tails laying by my whole, or there’s a school below me and I want to get down ASAP, I’ll just grab a tail. I don’t toss them down the hole.
Heads stay on the hook better/longer, there’s more bone and hard stuff for the hook to grab and they don’t disintegrate as fast.
The eye ball is also something fish may notice more than you think. You see bait companies using that image in baits now (I believe I just saw a Northland spoon with an image of like 8 eye balls on it – there’s a jig shaped like one big eye ball as well).
I’m not a fan of a whole minnow unless it’s a dead stick or tip up, hooked through the vent or dorsal. The action of the spoon is more important than the meat that’s underneath it. I’m often using smaller presentations (1/8 oz type spoons and UL rippin raps for walleyes). A while minor is just too big to get the right action in those lures. Also, when you’re getting a reactionary bite, I want that hook in their mouth immediately. Obviously, you don’t let them run with a jigging lure to make sure they get hooked up. I don’t want to run into fish coming away with nothing but a whole minnow and no hook.
At the end of the day, I’m sure it matters very little. Those are just my preferences.