I need to buy a new pair of fins. There are many choices, so I would like some technical guidance. I am savvy in the water, but not as strong as I was, so I would like fins that give me the most help for their inertia.

Thus, a very long fin does not seem good for me. I've looked at a split-fin, but don't understand the benefit -- the person showing it to me said it would increase maneuverability. I don't think this is my main concern. My main concern is conserving energy.