How to find a main

Everyone I talk to says the key to climbing in League is finding your OTP. One of my friends has proven just that crawling out of Bronze up to Plat 4 with almost exclusively Anivia. He has over 400k mastery points into her.

I have been trying to find a champ that I just love but I cant seem to do it. Any champ I play I can't do it for more than 3 or 4 games without getting tired of playing them. I have Level 7 on Fiora with 50k mastery points but like I said I can't play her over and over. I also have 70k into Twitch and 30k into Kindred.

From this I can conclude that I like champs that play liek assassins but don't have their inherent weaknesses: ultimate-reliance and being very squishy/melee. Anyone have suggetions for champs you find fun to play over and over?

I was thinking Casseopeia just because the couple of games I played with her were super fun and she matches my mold of being really bursty while also having alot of built in utlity. As well I'd have a champ for every role except support.

TL;DR Version: I like champs that play like assassins but arent assassins, like Fiora, Twitch, and Kindred. I get tired of playing the same champ over and over again, but want to find one I can do this with. I was thiking Cass just because I found her really fun and bursty even with all her utility. Suggestions?

And I do realize some of you are going to say things like "The key to climbing isnt getting good at one champ. What if they get banned?" or something like that. To that I say: Yeah I know. Please just give me some suggestionsthat are fairly off meta and not likely to get nerfed or buffed in the future.