Aatrox is always a good pick into any matchup if you know how to play it. If you get first pick and scared of getting counter picked aatrox is a good choice. Most of his matchups are skill-matchups so if you lose you could have played better in most cases. Not the easiest champ to master but not the hardest either. The diffrence between a good aatrox and a bad aatrox is that the good aatrox hit the skillshots. Good Aatrox players also play around their cooldowns to win matchups and they adapt their playstyle in team fights depending on the game and scenario. Aatrox takes a lot of patience and you have to know when you are being on the defensive and when you can play aggressive. Many people think aatrox is a clunky champion but once you've mastered him he feels very smooth and satisfying when you mix your abilites together fluently.

Laning phase: Aatrox can be played both aggressively and defensively in laning phase. If youre playing defensive. You want to slow push and set up freezes with aatrox and fight in your wave. You can play aggresive by perma shoving and poking enemy under tower if you are sure the jungler isn't close or zone the enemy from the wave. If you play vs a teleport or roaming champ perma push to put pressure. Aatrox can proxy sometimes since you can jump the wall with E and you have wave clear. If you get ahead early game you can put a lot of pressure on top side and force the jungler to come. You can often 1v2 and win if done right. When trading you have to play around your own and the enemy cooldowns. It's important to keep maximum distance between you and your enemy so you can avoid damage while still being able to deal a lot. Early game aatrox has long cooldwons so switch between defence and offense depending on your Q cd.

Mid game: Rotate to objectives and team fight for late drakes and early herald. In these fights you always have a diffrent purpose look tab and see what you need. When you are the only strong player on the team play in fog of war and try to kill the most important enemy first. If your ADC is fed you want to peel for him. If you have no engage you might have to go first et.c. Mid game is when aatrox is at his best If you get one kill you will just run through the rest of the enemy team and win. It's important that you don't lose your lead as aatrox or you will not come back until you're already outscaled

Late game: You get outscaled by most champs you want to provide as much cc as you can and get picks. Punish the enemy if they misstep and play with your team.

The most essential things to know:
You can flash while using Q
You can aa cancel with your E
Using Q right before getting hit by enemy cc your Q still goes through.
Holding onto your 3d Q instead of using it makes your Q come off cooldown faster.
You can E through a lot of walls with your E

I am an Aatrox OTP and play the champ everyday I only say what I know for certain from my own experience and I improve everyday from watching the best aatrox players and experiencing new ways to have the most agency with the champ. If you have any questions ask me live on twitch or dm me on twitter.
(You won't become good at aatrox just by reading this guide you need to actually practice alot on your own)