Darius is good for agressive players, you can play 2v1 at level 1, watch out for Yorick and Illaoi (your counters, ban'em)
I think Ragnaros is really fun, although it depends on your playstyle
good, but you dont writed how you are speaking lol champions.
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please note that this is just based on my opinion
Fiora:
A really strong duelist, can almost win every 1v1 due to her skill set, easy to use, need a perfect timing on her E.
Cho Gath:
Tanky, deals true damage, silence, knockup, very great sustain. Just be good in laning phase and get strong late game!
Darius:
Use his strong kits to get an early game boost! Easy to get fed early on laning phase, very simple to use, could win 2v1 easily when u hit 6, need a smart use on his Q.
Syndra:
Her R can delete squishy targets extremely fast! Use it early to kill their carry on a teamfight to get a 4v5
Fizz:
I'd say the most perfect champ to climb elo. Very high damage, can chase/escape really easy.
Rammus:
Really good jungle pick against strong DPS, easily taunt the DPS dealer on team fight and win.
Twitch:
Safe with his stealth, just stand back, ult and finish up the enemies. But dependant on your team's tanker and initiator.
Vayne:
Very very easy to use, really good at kiting and chasing, strong against tanks. Need good positioning