Without going into specifics of engineering and material advances, my instinct would be to buy the thing where if something went wrong with a seal or a closure,

Without going into specifics of engineering and material advances, my instinct would be to buy the thing where if something went wrong with a seal or a closure, the water would remain contained. Side loaders assume by nature that nothing will go so wrong that everything fails and water leaks out the front. If I was purchasing for harsh conditions and intermittent supply with standard Earth gravity, I, too, would choose top loaders.