After reading lsorenson's post, it set me to thinking and after watching this thread for a few days, I might have something to add.
Maybe the original premise here has some debatable algebra. First, understand that Hammerheads don't care much for great viz. That's not how they stay alive and hunt. They lurk.
Is it really a good idea to decide between Cocos and Galapagos based on Hammerhead sightings? After all, the question is posed as a one-or-the-other proposition.
A few folks understand that the holy-grail Cocos trip involves a protracted thrash in the form of a long sea trip to get out where the action occurs.
The Galloping Pogos is a stupid lengthy set of air flights, then it also involves a similar brutal liveaboard crossing to the North and Darwin/Wolf.
We like doing land based in the G after many years of liveaboards. We still see the Hammerheads, but not in the same predictable swirling schools as the 3x more expensive liveaboard- plus, we get to do the many land based excursions. It is equally a loss to go to the G and not dive as it is the other way around... not doing at least 4 days of land excursions. The same can not be said for Cocos.
After having experienced both ways, I believe I could take my last breath and be happy knowing that I did the Galapagos both above and under the water. My Cocos trip will not likely be a part of my last thoughts, even though the Sharks were indeed spectacular.
Maybe I'm jaded? It all depends on what gets you off. Okay, I'm jaded. But... My wife just started diving 13 years ago and has seen it all by now. On more than one occasion, she has slipped into the water and noticed swarming Sharks. After a look, she's not real overly-absorbed by the spectacle that completely captivates many other divers. After two encounters with Hammerheads, she was more entranced by the Mobula Rays. The gawk factor of the Hammerheads came and went pretty quickly, but one dive when she was going face to face with the Seals, a Hammerhead did scream through at 15fsw and 30mph. The difference between seeing them, versus the pure luck observation of behaviors.
Most group observations of schooling behavior are by divers at considerable depth. These Sharks hunt solo and in fairly shallow turbid water, where the divers generally are not. So this adds another wrench into the equation. After you've seen them for five dives in a row, what's next? Most dive plans avoid this shallow hunting ground because of the inherent difficulty of currents and underwater architecture.
Whatever you're wanting, whatever gets your motor running. But try not to be too focused on a "bucket list", sometimes it aint all that.
