https://rpg.stackexchange.com/questions/197639/at-what-level-does-each-class-get-its-subclass

Hexblade's Curse + Magic Missile works

https://summoninggrounds.com/5e-racial-stat-bonus-chart/

https://www.quora.com/What-are-the-most-powerful-saving-throw-proficiencies-in-5e-D-D

It's pretty much Con>Dex>Wis>Str>Cha>Int.

Fighter, Cleric (Knowledge, Life, Nature, Forge) and Warlock (Hexblade) give some of the best 1 level dip benefits. So that could explain their popularity, if this data includes multi-classing.

Fighters (Action Surge), Clerics (Tempest) and Warlocks (Invocations - Devil's Sight) also give excellent 2nd level benefits for multi-classes.

Dips:

A dip takes one or two levels of another class.

https://www.youtube.com/watch?v=AsXm8MVKT04

The Fighter (2 levels) - all armor, shields, STR/CON saves, all weapons... fighting style, second wind, action surge

The Rogue (1 level) - Thieves Tools, Expertise!.. Cunning Action at 2

The Cleric (1 level) - Light/Medium armor, shields, subclasses (Tempest, Twilight), spells (Bless, Guidance, Healing Word)

The Paladin? (2 levels) - Fighting Style, Divine Smite (for primary spellcasters, primarily Valor/Swords Bards and Sorcerers... even Bladesingers... Hexblade Warlock)

The Warlock (Hexblade) - Hex Warrior, Eldritch Blast and Hex, Medium Armor and Shields... Invocations at level 2

Bonus: Artificer (for Wizards), Sorcerer (for CHA casters, CON saves!)

Sorcerer might not be a dip.. 2 levels for sure (for Font of Magic), take Metamagic Adept (or a third level)

Barbarian (1 or 2)

Gloomstalker Ranger (3) on Fighter/Rogue