Any champion is viable in lower elos. What matters significantly more is general game knowledge. However, if I had to recommend champions to play in ranked I would tell you a few things.
1 - Pick someone that's easy. As a general rule of thumb, you'll climb much faster on champions like Volibear, Garen, Annie, etc than you will on champions like Yasuo, Lee Sin, Ekko, Zed, and others. However, I would say that this rule is not as important as the next one which is. . .
2 - Pick someone you really enjoy playing. You will learn better and climb faster on champions that you really enjoy playing, and there's no point to playing (even in ranked) if you're not having any fun. This over rule #1 as long as you don't care about how long it takes to climb.
3 - General advice - Since game knowledge matters more than picking the right champion (especially in silver/bronze), I'm going to give you some advice on mistakes I've seen players make that you should work to correct if you find yourself making them. The biggest thing I see that is probably the easiest to correct is
4: DON'T THROW YOUR LIFE AWAY. if you're dying an average of more than probably around 4-5 times per game, that's too much. Practice proper positioning, because it's huge. Don't go wandering in the jungle with no vision if you can only see one or none of the enemy team, don't engage team fights if you're the adc but stay in the back line and look for picks. Don't get too greedy in lane and consequently die over and over to avoidable enemy ganks.
and, last but not least, my advice for ranked
5: Learn from your mistakes and don't blame others. If you legitimately screw up, acknowledge it and learn from it. The mentality that most people that are stuck in bronze have is that they think everything is everyone else's fault, and that blinds them to the mistakes they make. It is not very hard to get out of bronze, learn from your mistakes and realize what you do wrong and you will climb.
Oh, and I know I said I was done but two more things -
1 - BUY AND USE THE TRINKET UPGRADES
2 - PRACTICE FARMING. A good goal to shoot for is, if you're in a lane, 70 cs by 10 minutes and at least double that by 20 minutes. It's not that hard of a goal to make, there are plenty of people that farm way better than that, but if you farm that well in low bronze you will easily out farm most others.
Good luck!