Depends on 2 Things.
- Your personal Mechanics.
- Your personal Play Style.
If you have a High Mechanical Skill... nothing better than 'abusing' High Mechanic Champions, as due to he complexity of play are allowed massive power. Champions like Zed, Lee Sin, LeBlanc.
Play Style will also go largely into Role/Type. Do you want to Dive? If so, Back Line Assassinate or into the Front Line break them? Would you rather Poke? Split Push? Pick Off?
Now, if Less Mechanical, but good with other things like Map Awareness and Shot Calling, there is a plethora of Basic Champions that are still strong enough to see Pro Play that you can Carry with.
Group 1 will be Mechanical Skilled, Group 2 will be Basic.
ADC
- Lucian, Ezreal.
- Ashe, Caitlyn, Miss Fortune.
Support
- Karma, Morgana, Zyra.
- Braum, Leona, Thresh, Taric.
Mid
- LeBlanc, Talon, Zed, Akali, Katarina, Azir, Anivia, AP Ekko, Kassadin.
- Cho' Goth, Xerath, Ziggs.
Jungle
- Lee Sin, Elise.
- Udyr, Xin Zhou, Master Yi, Sejuani, Jax.
Top.
- Vladimer, Irelia, Fiora, Tank Ekko, Riven.
- Shen, Olaf, Mundo, (Low Elo) Nasus.
There are more, but I think you can draw the correlations.
Also Off Meta Champions like Urgot can be a pain at Low Elo because most don't know how to defend against him. I remember the first time I faced an Urgot, he was ADC and I was our ADC. I assumed he just outranged me with Abilities because I didn't realize I was opening up his Passive by taking the first Ability which makes his shard homing with great range. We won, but my lane was wrecked and only my Team Fighting ability kept me from throwing. It was tough, because I had no clue about Urgot other than everyone saying he sucked.
So you can get some Teemo, get some Urgot... and learn when and how to abuse the enemy with them. Swain (more mainstream since Buff) and Kassadin as well.
It's really, at our level, less about WHAT Champion, and more about how much we master our Champion over the people we are facing. People say Zed is OP... but I personally suck at Zed so if I pick Zed their Mid should do well. Because they are better on their Champ than I am on the one I took. So Player Skill matters most at the Low Elo, where most aren't good enough for Meta to matter.
Guys like Tyrndamere, Olaf, Vlad, Urgot, Zed... vs. people that don't understand the basics of stopping them, completely wreck.
Split Pushers are also good, but require your Team. If you let Nasus Free Farm, he WILL become unkillable and 1 Shot everyone. But usually a Team will group and dive the Nasus, and his team won't push in response... so he's wasted. But you get with a group you can focus those Split Pushers and really shine.
Hope these suggestions help.