Personally, I think
and
are probably the most important supports to know since they are rather powerful and versatile. While Nautilus excels at initiating fights while Janna excels at protecting her allies (and blocking divers), both options have strong roaming potential and can adapt to different situations.
is a great option for sustaining through the laning phase and assisting your allies globally. She is exceptionally useful against team compositions which lack the ability to dive onto her and/or rely on poking your team down before fights.
is great for protecting your allies from harm and absorbing damage for them. While he can have issues in some match-ups, he can largely negate the threat posed by many champions if positioned correctly.
is useful against team compositions which rely on picks and/or have delayed damage since he can devour their target and protect them from damage. As such, he is great when the enemy team has champions such as Morgana, Lux, Elise or Zed. As added benefits, he is quite capable of fighting against many opposing champions alone, his Devour is great for killing Scuttle Crab and his ultimate provides significant amounts of map pressure.
is exceptionally useful against many divers due to her ability to protect her ally (bonus health, shield) and disable the diver (Polymorph, knock-up) until her allies can respond. As a bonus, she is useful against stealth champions (i.e. Kha'zix, Vayne, Akali) since her E provides true-sight of the target for its duration.
is great for picking and locking down targets due to her powerful CC (Q, ult), has decent sustain during the laning phase and can easily trigger Spellthief's Edge for additional gold and damage. However, her Black Shield is by far the strongest portion of her kit when used properly. If you have an ally whose main weakness is CC (i.e. Katarina, Master Yi, Vayne), then you can temporarily remove that vulnerability and let them tear apart the enemy team.
While it probably isn't necessary, having a damage-oriented support can be rather useful for those rare, rare instances where your team picks primarily low-damage and high-utility champions. Your best options for this situation are probably:
