This is my opinion on every single support in the game as of patch 3.3 (I ignored the - & + tiers to make it easier on myself)
Io: The best point ta...... I mean support in the game right now. The fact that you can have a 5 v 5 team fight while you are capturing the point (thanks to Luna) is what makes her OP. Her ult is like a weaker version of Khan's ult; Her best talent right now is Goddess's Blessing. Her healing is decent and not so high in terms of numbers but it is complemented by Luna.
Ying: The best healer in terms of numbers (In my opinion). She is really good with both aggressive and defensive comps. She works really well in a 2 support comp. For talents: Focusing Lens is great if you are playing as an Off-Support while Life Exchange is the best choice for solo support. Her ult is very powerful allowing you to heal the whole team at once.
Grover: Really good with point focused comps thanks to his area heals , also good in tight and small maps as he can heal through walls. His ult is very good as you can save yourself or your teammates with it although it can be nullified by cauterize. His best talent right now is deep root; CC has been dominating this patch and Grover's roots are among the best CC abilities. With the right build and team comp , he can heal , cripple and even damage very well.
Mal'Damba; Honestly Damba is in a weird spot. He is very good in term of abilities. He is one of the best supports at surviving. His ult is very powerful and can win you a team fight on its own; But the problem is his healing numbers might not be as impressive as his competitors. A good Mal'Damba player can out heal the other supports. In general people consider Damba to be the most balanced support in the game as he requires skill to be effective and think that the other support champions should be balanced around Damba's healing numbers. For talents: Mending Spirits is the best as it provides better heals to the team while the gourd is used on the point mostly; Wikono's Wraith is a good talent if used as an Off-Support.
Corvus: The latest installment to the support class. Corvus is really good with a balanced team (a team where some players are aggressive and the rest are defensive) where he can sit back in the backline while healing his aggressive teammates. His best talent is Spreading Influence as you can heal up to 3 targets as once with it. His ult is very underrated in my opinion as it can be very useful to zone the enemy team or heal the frontlines on the point. Where Corvus shines in my opinion is in his cards; He has a variety of useful cards , some of the most used ones are Grand Design , Crushing Expectations and Shadow Tribunal. He is very good at pocketing specially with his Dark Gifts talent as he can provide many perks to his marked target. Stunning Visage is not as good as the other Off-Support talents that the other supports have but it can be useful. In general Corvus is consider a good and balanced support. His healing numbers are good and he needs some training in order to master the mark rotation and heal specially with the talent Spreading Influence.
Furia: Still consider a very solid support despite the lower play rate. She is very good at team fights as she contribute with both heals and damage. She heals for a lot , deals good damage , can stun and has a powerful ult; why so low then? the answer in my opinion is that it is too much. Mostly Furia players are more aggressive in their play-style and with the nerf to her wrath , she loses fight more often now. I still consider Cherish to be her best talent as it benefits her style of play more making her very useful in team fights; On the other hand Solar Blessing surprisingly is very effective but not most of the time is it requires your point tanks to turn their attention to you in order to get healed by the beam and if the beam misses , at that point you would wish you had picked Cherish. In general she just feels as she doesn't survive as much as she used to do and her impact can be unnecessary if play in a bad team comp.
Jenos: The fallen god. Let's get this out of the way first , his ult is one of the best in the game and very fun to use. Now for his healing , it is actually a lot better than what people think. It doesn't have good burst but it stays for quite a long time which makes him good with DPS champions and ineffective with tanks. the Nerf to Light years (The range if his heal) meant that he has to be a lot closer to the fights now which he is not that good at. Luminary is his best talent by far as the extra damage can help your team win 1v1s and team fights easier. Lately people started using Binary Star instead of Luminary to allow him better chance at surviving during fights but in my opinion his heals are not that good without Luminary and if you play carefully , Binary Star should not be necessary. Overall he is still good with the right comps but can be shut down easily.
Seris: The soul support of beginners. She is very easy to play and throws out a lot of heals but is countered very hard by cauterize. Her ult is very useful and is one of the best ults in the game to combo with , but it requires good timing. Soul Collector is her best talent (despite being more useful for a damage build) as she can increase her health pool and deal good damage while healing her teammates although it is better in a 2 supports comp. Mortal Reach is the preferred talent for a solo support as it gives you more reach and duration on the heal. She can initially escape well but if someone chases her she is dead for sure.
This will be shorter than the others as I consider D tier as "too bad to be used" tier
Pip: Mega Potion doesn't provide enough healing while both it and Combat Medic require a lot of skill to learn the arc of the shoots to be able to heal consistently. He is pretty much unable to heal targets who are in the air. Preferably he is used as an Off-Support more focused on damage with his talent Catalyst. His ult though is one of the best in the game and can win team fights on its own.
Grohk: Only play him as damage with Maelstrom the end. His totems while having decent healing numbers are very hard to place correctly which makes Totemic Ward useless. Spirits Domain can be used effectively but pretty much every other support would be better. His ult is the best thing going for him but it can be shut down thanks to cauterize.