I think two blades is enough and don't want the weight or thickness of more, or for the blades to be thinner to accommodate more than two. With two blades, I use the smaller for utility (opening boxes, whittling, day-to-day tasks), and keep the larger continually sharp and clean (no adhesive residue or tree gum). A one-blade knife is just as suitable but more discipline must be exercised to keep it sharp in spite of the variety of uses.
I prefer the spear point and its flat grind (as on a Canoe) over the hollow-ground clip point of a Whittler, Peanut, or Trapper, but the pen blade is the one I use the most frequently and for the widest variety of purposes. The pen blade can open boxes, whittle a feather stick, cut a branch off, slice fruit, cut a cluster of grapes off the vine, open an envelope, sharpen a pencil, dissect a seed, whittle a spoon or fork from a twig, jimmy a simple lock, turn a screw, clear out a brass cartridge, clean a primer pocket, trim a plastic nose off a tube of glue or caulk. Why I can't think of much anything a pen knife can't do other than easily fell a wrist-thick tree or limb a downed tree. I suppose owing to its short length it's not the best for cutting your steak. Those purposes are better served by an ax or hatchet and a fixed blade that is washed with the dishes. The pen blade would leave you wanting for self-defense purposes, or to skin a buck or dress a hog, but for many of us, those are once-in-a-lifetime uses. There is no small or medium sized folder that wouldn't leave us equally wanting for any of those purposes for which a pen blade is not quite suitable.
So I'd have to say the pen blade is the most useful traditional blade for day to day use. The reason the Peanut works is because it is so equipped, and even offers a surplus of an additional clip point blade. Therefore, it's really more knife than most people will use.