I know Arsenal are absolute home favorites over Manchester United, but I never expected Arsenal to beat Manchester United as easily as some people think. Manchester United have not been too bad in the last 3 matches, but I think they need to prepare their defense well. Of course Arsenal has a very good attack line to face Manchester United's defense, but I don't expect Arsenal to easily penetrate the defense and score goals.
I agree with you that Arsenal vs Manchester United is the most anticipated game of the weekend and it will be the most thrilling game. Arsenal have a high probability of winning, but that has never guaranteed them a win this week.
Arsenal is the favorite because they are at home but to me, Manchester United is a better team. Although United is facing some injury woes they still have some players that will compete favorably with the Arsenal team. I also think that both teams are on the same level having won two games but United has lost one game making them to be in the 8th position with 6 points. We expect to see an entertaining match and both teams will do everything to get these three points in this game. But there is also a possibility that this game will end in a draw.
From the performance of these teams, one might assume that Manchester City has a more organized and established team. Their new players easily blend with the teams maybe it might be because of the managerial mastery of Pep Guardiola. City has won three games in three, scored six goals, and conceived just one, what an outstanding result for the reigning EPL champions.