PSG won't be favorite in London, but PSG is better than Real Madrid.
Real Madrid can't win big margin even met against mediocre teams, while PSG able to humiliate the opponents. Arsenal do have a good history, but sometime Arsenal is not consistent during big match.
The first leg Arsenal will win I think.
Hopefully Arsenal can win the first leg at the Emirates and at least 2 goals even though PSG also scored, but the bad news is that Arsenal is experiencing a storm of injuries before facing PSG and among some of its best players and this is what is feared because if the result of the first leg Arsenal only gets a draw or only a difference of 1 goal then in the second leg Arsenal must really play aggressively to pressure PSG players in order to win on aggregate. But behind Arsenal's inconsistency, Arsenal has a very good defense like in the match against Real Madrid and makes Real Madrid players frustrated and often commit violations.
Everyone seems so comfortable concluding that Arsenal will win PSG but they are forgetting some important things. I understand that Arsenal have won PSG this
year so people are thinking such will easily be repeated but that is what I even consider a factor that will favor PSG. Recur that Barcelona defeated Borussia Dortmund first leg, but the second leg, Dortmund revenged and won Barcelona. The same thing happened between PSG and Aston Villa and that is likely to happen between Arsenal and PSG. I will not be confident to bet on this but it is a possibility.