Never been to the Galapagos but have been to Cocos twice and Socorro once. Headed back to Socorro this coming November.
The single best dive I have ever done was a baitball dive in Cocos. The best dive trip I have ever been on was Socorro. We saw it all in Socorro. Mantas, dolphins up close, sharks including schooling hammerheads, rays, and whale sharks.
Socorro is getting crowded. Quite a few boats go there now. I like the Rocio Del Mar. Great operation and probably the best crew of any liveaboard I have been on. But the best part is they start their trips in November while most of the others start in December. The first time I was in Socorro on the RDM we only saw one other boat the entire time we were there and that was in November. I can highly recommend a November trip on the RDM.