Someone did some research into things, and Dual Wielding is definitively the best, for the following reason: Both weapons get the benefit of both weapons' enchantments.
Let's say you have two weapons, each with an enchantment slot. Each one has Increased Damage 10 on it, giving +27 to melee damage. When dual-wielding them, Each one gets the benefit of both weapons' +27 melee damage, therefore each gets a bonus of +54 melee damage. That means you get +108 melee damage total, as opposed to any other type of combat, which would only give you +27. So you're doing, on average, four times the damage.
Any melee damage boosting charms also apply to both, so if you stacked, say, 3 Divine Damage Charms, which give +10 per, you'd get +30 to each weapon, or +60 total.
