I used photon pun 2! :D It's really easy to use and there are several tutorials on YouTube! And it has very good documentation! However, you will be limited to a maximum of 20 players. If that's not a problem for you, go for it!
However, I started using Fishnet! It's a free alternative, you can have even more players and it has an active community that can help you!
I hope everything goes well in your game development!