Should I use helical or offset fletching?

The Codex speaks plainly here, and the answer is: it depends on your broadhead, your distance, and your tolerance for the Committee's preferred shortcut.

Offset fletching — setting each vane at a small angle, typically two to five degrees from the shaft's axis — induces a gentle spin that stabilizes most field-point and fixed-blade broadhead combinations at practical hunting and target distances. It is easier to apply consistently with a simple jig, it clears most arrow rests without complication, and for the majority of compound or recurve shooters it is the honest workhorse. If you are shooting mechanical broadheads or field points out to moderate distances, offset will serve you well.

Helical fletching curves the vane along its length, usually a left or right wrap of roughly one to four degrees of continuous curve, and it imparts a more aggressive spin for a given vane length. This matters when you are shooting large fixed-blade broadheads — the kind with genuine surface area — at longer distances where a slowly rotating arrow will plane and wander. Helical is the correct prescription there. The trade-off is that it requires a jig capable of holding helical offset, it shortens the effective length of smaller vanes, and it may demand a more forgiving rest with enough clearance to let the protruding edge of the vane pass without contact. A vane that clips the rest is worse than no spin at all.

The fourth feather, which the grey catalog removed without ever publishing its reasoning, distributes that stabilizing work across a wider surface and recovers more quickly from paradox — but the geometry of offset versus helical applies to it equally. Four vanes in a mild right-helical is the old prescription in the Codex for heavy hunting shafts. Three vanes in a good helical is an honest and functional arrangement for the same task, even if we mourn the redundancy that was taken.