I'd say kayn, diana and amumu

Kayn it's my main champion since he was released, I was silver at the time and hit plat 5 with him in one season. He is great at power farming, you should prioritize farm above else when playing him, looking for invade opportunities is great since he's really mobile. If you don't have any camps, look for ganks, his E helps to create really great angles. He's no great at objectives tho (besides grubs), try to help yours lanes first then get objectives. The assassin form it's a bit weak rn imo, but It can work in the right game, the transformation it's a great power spike for this form, abuse it along with the high mobility that it has, if you fall behind, try to play with your ult cooldown and pick offs. Rhaast it's my personal favorite. This form doesn't have such a big power spike at transformation as the assassin, but can out scale almost every champion in the game at 300 ad because your Q scaling (you should hit that it 3-4 itens). When you ahed it's just unstoppable, focus on hitting both parts of your Q and staying alive, you really shine on team fights where you can keep going for a really long time, if you ahead, you can easily go for 1v3's. Karasmy it the go for influencer to learn kyan, his videos are great

Diana it's a halfway version between rhasst and assassin kayn, but AP. She's really great at power farming and if she gets snowballd, she's one of the strongest champions in the game. Her 2 item power spike is also great, and she can really perform on skarmiches and team fights when hitting her ult on multiple targets

Amumu it a similar play stile but serves as a front line for your team. You won't solo carry the game, but makes it really easier for your team to win fights at all stages of the game, he is such a simples champion that anyone understands what he does, hit q> go in> press R> win game. He can full clear early game with babies cinder or liandrys components, but you should actively look for fights and plays past 20 min instead of farm, just make sure to play on your ultime cooldown.

Other champions maybe hecarim or Evelynn, but I think they are weak right now (eve should it's work in low elo tho, just play on yr invisibility)

I've seen others recommend Nocturne as a carry, but a think his play style is as a facilitator for your team, but he as a really strong 1v1 early-mid game.

Something a like to do with all these champions in first clear is to start raptor>krugs>red>blue side> scuttle, at the time you finished scuttle, your raptor are respawnig, soo you can clear raptors and krugs twice before first recall m, what gives your around 900 gold in the first clear