When telling a friend “according to the news, tomorrow looks like rain” which of these sentences is correct?
The top one is used when someone is giving their opinion. In this case, the verb before そう is the plain-form or 辞書形。
The latter one is used when giving your own opinion based on observation. In this case, the verb before そう is the masu-form or ます形。
So the first sentence is the correct one.