Current Tier list:
Depending on the meta and patch that RIOT implements in League of Legends the tier list can easily be changed. With patch 12.15 here are some of the best possible champions and lanes to boost your rank and MMR. If you are main adc or support we would suggest finding a duo that can play alongside you as that can help a lot. While the top lane is important and you can easily carry with some champions that can snowball hard if they get a lead early on it is much harder to control the rest of the map as a top laner.
Tier list sorted by roles/lanes
Lower-ELO LoL Tier List for Patch 12.15:
Top Lane Tier List:
Top: Optimal (S-tier / God-tier):
Aatrox, Ornn, Darius, Mordekaiser, Shen, Poppy, Garen, Olaf, Wukong
Great (A-tier):
Camille, Riven, Fiora, Kled, Lillia, Vayne, Akshan, Illaoi, Sett, Swain, Urgot, Jax, Quinn, Sejuani, Shyvana, Yorick
Good (B-tier):
Gangplank, Gnar, Irelia, Gwen, Yone, Gragas, Kayle, Renekton, Singed, Tahm Kench, Dr. Mundo, Nasus, Teemo, Trundle, Tryndamere, Warwick
Jungle Tier List:
Optimal (S-tier / God-tier):
Fiddlesticks, Amumu, Diana, Master Yi, Rammus, Trundle, Volibear, Warwick, Zac
Great (A-tier):
Ekko, Kha’Zix, Rek’Sai, Shaco, Bel’Veth, Kayn, Poppy, Jarvan IV, Nunu + Willump, Shyvana, Olaf, Wukong
Good (B-tier):
Rengar, Ekko, Kindred, Lillia, Taliyah, Gragas, Graves, Mordekaiser, Viego, Udyr, Nocturne, Sejuani, Skarn, Vi
Mid Lane Tier List:

Optimal (S-tier / God-tier):
Sylas, Anivia, Viktor, Ahri, Swain, Vex, Zilean, Diana
Great (A-tier):
Katarina, Zed, Cassiopeia, Ekko, Taliyah, Talon, Xerath, Yone, Akshan, Heimerdinger, Galio, Kassadin, Annie, Veigar
Good (B-tier):
Akali, Azir, Aurelion Sol, Irelia, LeBlanc, Yasuo, Orianna, Vel’Koz, Vladimir, Fizz, Kayle, Pantheon, Lux, Malzahar, Neeko, Seraphine
ADC Tier List:

Optimal (S-tier / God-tier):
Jhin, Twitch, Sivir
Great (A-tier):
Draven, Nilah, Samira, Vayne, Heimerdinger, Karthus, Kog’Maw, Swain, Ashe, Miss Fortune, Seraphine, Veigar
Good (B-tier):
Ezreal, Kalista, Yasuo, Zeri, Cassiopeia, Kai’Sa, Lucian, Caitlyn, Varus, Jinx, Tristana
Support Tier List:

Optimal (S-tier / God-tier):
Renata Glasc, Bard, Senna, Taric, Zilean, Blitzcrank, Janna, Nami
Great (A-tier):
Vel’koz, Xerath, Alistar, Lulu, Swain, Amumu, Brand, Nautilus, Sona, Soraka, Yuumi, Zyra
Good (B-tier):
Pyke, Thresh, Rakan, Braum, Ashe, Karma, Leona, Lux, Maokai, Morgana, Seraphine
While this is a tier list seen from the eyes of most players it does not mean that you can’t play something that’s out of meta. There are a lot of combos that still work pretty well even if they are not on the list.
One of examples would be an adc Karthus with Senna as support, as you have decent ap as well as ad damage.
It also depends a lot on the situation and enemy champions as some champions just counter others no matter what, it is good to keep that in mind as well.
High-ELO LoL Tier List for Patch 12.12:
Best Top Laners for High Elo:

Optimal (S-tier / God-tier):
Camille, Gangplank, Riven, Fiora, Darius, Poppy
Great (A-tier):
Gnar, Rengar, Aatrox, Gwen, Kled, Ornn Akshan, Gragas, Mordekaiser, Shen, Jax, Olaf, Quinn, Shyvana, Tryndamere, Wukong
Good (B-tier):
Akali, Irelia, Sylas, Yone, Illaoi, Kayle, Kennen, Renekton, Sett, Singed, Swain, Udyr Cho’Gath, Garen, Malphite, Teemo
Best Junglers for High Elo:

Optimal (S-tier / God-tier):
Kindred, Rek’Sai, Fiddlesticks, Poppy, Diana
Great (A-tier):
Nidalee, Qiyana, Rengar, Elise, Kha’Zix, Taliyah, Bel’Veth, Pantheon, Viego, Udyr, Nunu + Willump, Skarner, Trundle, Voibear, Wukong, Zac
Good (B-tier):
Lee Sin, Zed, Evelynn, Ivern, Lillia, Shaco, Talon, Gragas, Graves, Kayn, Jarvan IV, Olaf, Rammus, Shyvana, Xin Zhao
Best Mid Laners for High Elo:

Optimal (S-tier / God-tier):
Katarina, Qiyana, Sylas, Swain
Great (A-tier):
Aurelion Sol, Azir, Yasuo, Anivia, Orianna, Talon, Viktor, Yone, Ahri, Akshan, Galio, Kassadin, Vex, Zilean, Diana, Veigar
Good (B-tier):
Akali, LeBlanc, Irelia, Zed, Zoe, Ekko, Cassiopeia, Rumble, Twisted Fate, Vel’Koz, Vladimir, Gragas, Seraphine
Best ADC for High Elo:

Optimal (S-tier / God-tier):
Draven, Jhin, Twitch, Sivir
Great (A-tier):
Ezreal, Kalista, Zeri, Kai’Sa, Nilah, Samira, Vayne, Karthus, Kog’Maw, Swain, Ashe, Jinx, Miss Fortune, Seraphine, Veigar
Good (B-tier):
Aphelios, Yasuo, Cassiopeia, Lucian, Caitlyn, Varus, Xayah, Tristana
Best Supports for High Elo:

Optimal (S-tier / God-tier):
Pyke, Renata Glasc, Bard, Senna, Taric, Janna
Great (A-tier):
Rakan, Alistar, Lulu, Zilean, Amumu, Blitzcrank, Nami, Nautilus, Seraphine, Sona, Yuumi
Good (B-tier):
Thresh, Vel’Koz, Xerath, Braum, Tahm Kench, Karma, Leona, Maokai, Rell, Soraka
Disclaimers:
- The tier list is made based on most played champions with the highest win rate over all. In case there are champions or champions you love to play are not on the list this does not mean that you should stop playing them. Mastering some of the champions up to perfection can prove that you can easily climb and win games with them even if they are not at the top of the tier list currently.
Those are the tier list of champions regarding solo que. And while there might be some overlap with pro play and 5v5 queue, unlike in solo you can expect a lot higher coordination from your teammates, and you know what you can expect from them unlike when you play with 3 or 4 random players in solo/duo queue
- If you wish to boost yourself as well as boost your MMR, focus on some easy/medium hard champions to play that are in S tier right now as that is the easiest way you can get your account to elo that you want to get.