It's Pikachu without a doubt. Even from a design perspective, you could bare Pikachu down to just the shape of the head with the red cheeks and most people would be able to pinpoint who it is, or at least say it's the Pokemon character - that's the true sign of something that is iconic. Link just doesn't have that reach. Maybe people outside the gaming sphere have heard of Zelda, but Link simply doesn't have the recognition as a visual icon. The multiple Links and designs doesn't help in establishing that brand either.
Even if the question boiled down to Zelda vs. Pokemon, I think nobody would argue against Pokemon there in terms of mainstream/universal appeal.
Surskit
Hi! I like shorts! They're comfy and easy to wear!