@pharaoh might be a great person to reach out to - I know they recently did a Group Session to cover how to pick your primary characters and strategic ways to master your main - he might be a perfect resource for you.

Just speaking from my own experience I’ve found dedicating my time to one or two characters really helped me improve a ton. Trying to juggle many characters always took my focus away from mastering the few. G&W, sonic, and cloud are all great choices though. I've been working on honing my cloud as well. And it also just depends on what you want to do. If you want to compete and win, best to really focus on knowing one or two characters really really deeply. If you just want to have fun, play whoever you like!