I think most of you are already aware of that but this advice is targeted to those who usually don't watch Twitch streams.
If you want to know which decks you most likely gonna face I'll recommend you to havea look on which big streamer is live at the moment and which decks they're using in this particular stream.
Sure a lot of player are trying the decks on YouTube but a great amount of players are also using what's up-to-date and not already uploaded anywhere.
As an example: Speci plays alot of Mill because he has fun with it and he always optimiseshis deck. I watched a bit of his stream today and went playing later on and guess what:
I played 5 times in a row against his new Mill variation.
As a side note: This is no hate against certain kind of decks and streamers. I'm completely fine with that and it also helps to keep the fun going because players get new variations of decks almost everyday to play with. This is just an advice to help out a few of you who might not be aware of that, so they can prepare a little bit.