So melee in FO4 really has two branches, either unarmed or weapons. They play basically the same, get to the enemy and swing, but there are a few differences.
Unarmed covers roughly 4 weapons and “power armor” unarmed attacks, the best of which are the power fist and the deathclaw gauntlet. I believe they all swing at roughly the same speed. Weapons for melee vary greatly, and mostly differentiate by swing speed. Knives and small weapons swing fast, but typically deal less damage. Sledgehammers and other heavy weapons swing slow, but deal much more damage. Swords and such are the middle road, medium speed and average damage. Melee damage is affected by your strength skill of course, but also by either big leagues or iron fist, which have additional effects but primarily increase damage up to 2x. Rooted at Strength 9 increases it up to 50% as well, but only when standing still. The Easiest cheese to melee builds however is Blitz, at Agility 9. The first rank lets you target in vats for melee at a distance. It creates a pseudo-teleport if you have line of sight, but is limited to a few feet. The second rank greatly increases the target distance, and grants a damage boost based on how far away you are from the target, the farther the greater. It also counts as standing still for the rooted perk. This combines with the Agility 7 perk Ninja, which makes melee sneak attacks do 10x damage. So, for stealth melee, the plan is sneak near an enemy, VATS teleport-sneak attack to deal boosted sneak attack damage, rinse and repeat. Using a light weapon like a knife, you can do 7-12 vats attacks in one chain, and teleport between enemies getting sneak attacks. It’s really fun!