One of the fixtures for the UCL round of 16 between Arsenal and Porto is more of an average probable game. Both teams are likely to win. Although Arsenal are a better side judging from their EPL performances, to their group stage performances too. Porto themselves aren't doing so bad in their league and they've got good track record in the group stage. That's why the game is going to be a little bit tough to predict the winner, well let's see if Arsenal would be able to comfortably win them and qualify for the next round.
Even if many people predict that Arsenal will win this match, in my opinion the match will not be easy for Arsenal to get full points. Porto have qualified 23 times for the Champions League and that means they are only behind Real Madrid and Barcelona in the Champions League and Porto have also won the Champions League twice. Even though that was before, Arsenal cannot underestimate Porto's performance because if they are careless, Arsenal will fail to advance to the next round.
Away matches will usually be much tougher because the Champions League is quite different from the main league so it is not uncommon for many clubs to be eliminated quickly. Arteta needs to prepare a lot of things because the match is still long and maybe he can motivate his players to perform as well as possible to get full points.