By the way you are kinda getting joke answers because its such a broad list of options which doesn't really make sense, generally in 5e you can't pick out a weapon and grab it, and if your DM has granted you this, they usually slap some restrictions on it. There are some VERY powerful swords which might win the fight for you.
Vorpal - Roll 20 on an attack, OFF WITH HIS HEAD!
Sword of Kas - All sorts of bonuses, (some random) if you keep your sanity..
Blackrazor - Free haste and tons of free hp with every kill
Moonblade - Potentially a +3 finnesse, throwing, keen, vorpal, spell storing sword..