D&D 5E The best 1 level dip for fighter?

[Volund]

Have you considered taking a feat instead of a level dip? You won't get everything you might have from the dip, but you might get enough to fulfill your character concept and you won't delay leveling up in fighter to get goodies like Extra Attack. For example, dipping rogue gets you a skill, expertise in two skills, thieves' tools and Sneak Attack, but he Prodigy feat from XGtE would get you expertise in one skill and a tool or language proficiency. If you're looking at caster classes, Cleric isn't a bad choice for a fighter since you want Wis anyway, but taking the Magic Initiate (Cleric) feat would at least get you one spell and two cantrips. I would take Protection from Evil and Good, which isn't great for most casters because they have better things to concentrate on, but for a fighter it's awesome. Aberrations, celestials, elementals, fey, fiends and undead all have disadvantage on attacks and you can't be frightened, charmed or possessed by them for 10 minutes, with no save except your own Con save if you take damage. Asking for divine aid before you make a strength check to climb, jump, lift or smash wouldn't be out of character for any martial class so Guidance seems appropriate for one of the cantrips. The other cantrip could be just about anything for martial flavor. Use Mending to repair broken arrows. Touch a fallen companion with Spare the Dying as you stand over them continuing to fight. If you have Intimidation you could use Thaumaturgy to augment your intimidating words with a booming voice or make a door behind someone slam shut. Light is always useful even if you have darkvision.