Arsenal is a good choice better than Manchester United because they are already doing well and with a striker now they should be able to challenge properly for the league title now. With Manchester United things will still be tougher because the entire team still struggling to find their feet so Arsenal is a good choice.
First time you are saying something about Arsenal that picked my interest, other times you are sentimental and bias.
Since you have made your review on both club I sure agree with you. Manchester United had their striker last season but have not been performing well. On the other hand, Arsenal were very close to the Champions League final without a proper striker. I believe Gyokeres will bring positive changes in the league. Also the depth of players they have now will allow flexibility and rotation of players properly.