Spiky lashes separate into points, wispy lashes blend into each other
A spiky band groups its hairs into distinct clusters with visible gaps between them. A wispy band mixes lengths so the hairs feather together and no single point stands out. Everything else follows from that one difference.
Spiky reads as drawn linework, which is why it matches the source material
Anime eyes are drawn with a few deliberate lash strokes, not with dense fringe. Spiky lashes reproduce that on a real face. If your reference is a screenshot, spiky is almost always the closer match.
Wispy survives close-up photography better
Under a phone camera at arm's length, the gaps in a spiky band read as gaps. Wispy keeps its texture at that distance and still looks like lashes rather than like a strip. Choose it when most of your photos will be portraits.
Your eye shape changes the result more than the character does
On a hooded or deep set eye, a heavy spiky band sits on the lid and hides it. Wispy keeps the lid visible and the eye open. Try the style on your own eye before you commit to it for a costume.
Spiky for stage and distance, wispy for a full day up close
Spiky wins where people see you from more than a metre away, including stage work and group photos. Wispy wins for a long convention day where most of your interactions happen at conversation distance.
Quick tip
If you cannot decide, cut a spiky band in half and wear it on the outer corners over a wispy base. You get the graphic tip and the soft inner half.