Hey!
From my own personal experience in bronze, jungle and support are the hardest to carry with. Not saying it cannot be done, but i probably could not carry myself out in those roles (Only G4 right now anyway). Back in season 5 I was placed in B4 ,and was pretty angry. Didn't think I deserved bronze, my teams are impossible to carry, etc. After a month or two of crying and blaming everything and everyone, I finally just said "y'know, I'm here for a reason. Lets find out what that is."
First I decided to play adc. This was back when Lucian was top tier, so i decided to just play him. For two reasons: first, I was finding that I was losing a lot of my games due to having an adc that cannot position. At 50 min into a game, that pretty much guarantees a loss. Figured I'd just do it myself. Second, Lucian is was hella strong. Win lane with my duo, and then steamroll mid/top/the game. After practicing in normals, I brought him to ranked and went on an 18 game win streak from I believe B3-S5. That was it. I probably got lucky, my duo carried me, whatever, but it worked.
I heard a streamer (cant remember which one) talking about how in solo q, the most important thing is pressure. If your bot lane loses tower early, and the enemy bot starts roaming, low elo doesnt know how to rotate/counter pressure so your ADC can catch back up. This happens to me all the time not matter what elo. Same for every lane. If your Jg gets behind, the smite disadvantage becomes huge as you lose dragon after dragon after baron cause you have no objective pressure. If your mid laner is losing to one that can roam and APPLY PRESSURE its a nightmare for the other lanes. If the enemy support is somehow a god alistar or something and is constantly roaming but you cant kill the enemy adc solo, your team gets rekt. So, try to pick a champ for the roles you play that can apply pressure easily.
Top:
Jg:
Mid:
ADC:
Supp:

Honestly any champ played right works, but these are some of my favorites to see in ranked, as they have either generally strong waveclear, suitability, roam potential. All part of applying pressure.
Sorry if this is long or unhelpful, first time posting on boards. Feel free to add me in game if you wanna practice or whatever.
Good luck![slayer-jinx-catface]