An ongoing debate on bullet design .......
Worst (and most common) design mistake: long unsupported nose. An unsupported nose will slump to one side in the barrel and cause poor accuracy (exception: some soft alloys may obturate enough to make an undersize nose fit the barrel, especially with black powder).
Worst design mistake for leverguns not carefully considering feeding and chambering requirements. Levergun cartridges have to be crimped and have to be a certain COL, so the bullet nose has to be carefully designed to cycle through the action and chamber.
Why don't jacketed bullets have grooves ? Because jacketed bullets are swaged. They would probably shoot better if they had grooves.
Why don't paper patched bullets have grooves ? Because paper patched slugs were traditionally made by swaging. Grooved paper patch bullets shoot just as well if not better.
Why don't saboted bullets for muzzleloaders have grooves ? Because they are made by swaging. There is no reason grooved bullets of the correct diameter can not be used with sabots in muzzleloaders.
What is your favorite design ? Every gun is a little different, but when cycling through an action is not a big issue, I like a short nose, a long body, and lots of bands and grooves. Basically a Loverin except with longer grooves and an even shorter nose.
Why do people crimp bullets for single shots ? Beats me. It's usually better to seat the bullet out to lightly kiss the rifling and never mind the crimp groove.