How I tell what is good right now.
https://i.gyazo.com/99d603f10d014f4efc4a01e187dbb205.png
This is a picture from the statistics page on OP.GG.
From the picture, you can see that champions like Yasuo, Jinx, Ashe, Soraka, and Janna all have high winrates and playrates. This means that they are consistently performing well, and aren't just 1 tricks who are able to play extremely well.
You can also see that champions like Pantheon and Kayle are both really good flex picks. These are the type of champions who you can go into ranked as a one trick and not fear having to play an odd pick, you will almost always get your champ because they can play multiple roles well.
#Pay attention to more than just winrate when you look at stats, otherwise you'll think Sion support is the best support or that Pantheon has a 60% winrate mid.