Wolfenstein

I found that the easiest way to get a 1 hit melee kill 100% of the time (on average enemies, not bosses of course) is to upgrade the Karabiner 98 with a bayonet and stab away. For even easier kills, use the Mire veil power at the same time.

Easy difficulty is pretty much auto beat-downs. I would suggest Evans' Bayonet as it is the fastest way, Mire makes the enemies react slowly and if you want to use veil at the same time you run faster closing more distance meaning less damage done to you while you charge your enemies.

Even before this though you can get many beat downs on scientists and weak normal Nazis as you play through the campaign to get started, especially on easy considering you are practically a tank. Don't rush too hard though as you are by no means invincible. Not that this matters unless you are going for less than 3 deaths this same playthrough.

Melee attacks with the Tesla Gun are the way to go: a quick burst of electricity from the TG will almost always stun low-level human enemies, at which point you can dash up and melee them to death while they stand there twitching.

For even better results, purchase the Tesla Gun updates that allow you to fire out more arcs and give off a burst of electricity when you melee, respectively: you can stun a small group of enemies and then quickly melee each of them for a one-hit kill on Easy difficulty.