Frozen Octopus or fresh Octopus for recipes?
This is my favorite reference for octopus.  Near the end, Harold McGee considers the fresh v. frozen octopus debate.  His results are not exactly conclusive. McGee found fresh octopus, lightly blanched, to be "sweetly scallop-like and not too chewy.  But cooking it turned it bouncier than ever." His conclusion: "Freshness isn't the key to relevatory octopus."  So, based on my reading, if your preparation only requires a light blanching and thin slices, go with fresh.  Otherwise, you are better off considering the cooking technique as the most important variable.