Maining A Champ

Okay, so i've been having this problem for a while, and I think it might be the reason why I am losing games. I cant stick with once champion when playing solo queue, I am always changing at the last minute, not sure who to pick. So I watched a few videos and most of them told me to make a list of champions that either fit my playstytle or I have fun with. My list included both and I ended up choosing 4 champions: Rengar, Zac, Zed, and Fizz.

I chose Rengar cos I enjoy oneshooting people, I like jungling, and I have fun with him.

Zac is by far my favorite champion in terms of design, he's really fun to play as support or jungle and I like how easy it is to disrupt teamfights with him.

Zed is pretty difficult to play but I am starting to get the hand of him, and I bet if I played him a bit more then I do now I would be doing ALOT better. I love how he can easily outplay people and burst. Also really fun...

And finally Fizz, real fun, can dominate teams, and has my favorite skin yet.

Ok now that I listed who are the candidates for my main champion, which do I pick? The one I have fun the most with? The one I dominate with? Do I main them all? Pls help.