theres no best any champ, its all about how well you play it vs how well your enemy plays theirs.

My main support is actually Karma. If you play her right, she has an instant ghost for you and one ally, a shield, a nuke, a huge aoe damage/aoe heal, and simply cannot be stopped latr in the game. She can easily turn a team fight around with her heavenly wave and your arc can start to really REALLY tower dive at level 4 with little to no worries. Most people make fun of her or say she's boring but she Ia literallly one of my favorite champions to play. I'd say my top 5 supports are Karma, Zilean, Soraka, Janna, and Lulu. Nami isn't that good imo. Ans its really hard to pass up Zils global exp buff. But Karma is my fav without a shadow of a doubt. I've never lost a game with her (normals, that is. She is also a beast ranked)

Best support would probably be blitzcrank unless you are paired with a downie who cant land skillshots.
Leona is also good cause she has tankiness and 3 stuns.
Taric is decent cause he basically has an innate aegis.
Alistar works quite well cause he has sustain, cc, disengage.
Nami is great cause of sustain, disengage, cc, she's like less tanky alistar.
Those are the best supports.
Zyra, Lux, soraka and janna are okay. Volibear is pretty niche but he can work as well.
I would suggest mainly playing taric, alistar, nami, leona and nunu as support because they're strongest. And because tanky supports are pretty useful for meta game

I main Janna and think she is the best throughout the match. Her shield gets ridiculous late game, and a well placed ult can change the team fights.

I get yelled at for trying to pick zilean support =(

If you're looking for a good anti-counter, go with Alitstar.

Lulu.

Sona

Any support is good it all comes down to are 5 factors.
1) Player skill (this is a big factor)
2) Opposing team skill (also a big factor)
3) ADC champ pick ( always look for synergy)
4) Again ADC (Player) ( are they aggressive or passive? Concerned with CS or K/D? )
5) Counterpick ( I rank this lowest factor due to personal preference always affecting champ selection)

I'm a big fan of support morg and shen.

Best support is one you play great, accoroding to your skill set... everyone can say ohh this is better, than this, or this is better than that.... I love everyone saying Taric is the best (I eats him up).

But really when it comes down to it, who you play best is how you spec him/her... not what people say spec as... but what you feel is good