The maximum effort that Porto, Shakhtar and Antwerp can make is to hold Barcelona to a draw in the remaining three group phase matches, the rest or let's say beating Barcelona seems quite difficult for these three clubs. I think it is very clear now that Xavi squad is guaranteed to qualify as group H winners, and I predict that in the next three matches they will again be able to secure full points.
It is clear that Barcelona meeting with Bayern Munchen is one of the most awaited ones, and is an ideal match because both are considered the favorite clubs to win the UCL trophy this season. Although it's too early to say, I predict one of the two clubs will enter the final. I also understand that many surprises could happen in the future, especially if you see that many important Barcelona players are currently suffering from injuries.
Now with the current situation we can't expect good result from the Antwerp and Porto against Barcelona because Porto will be play away and Antwerp is not having enough quality to stop the Barcelona even they are playing at home which will give good advantage to Barcelona for the staying at the op and Shakhtar is difficult side with they can hold, but this is also not having good chance I have personal feeling most chances Barcelona could be stood at the top without losing any match.
Maybe this could be ideal match for you but for me this could be Bayern Munich match because they are having much better squad which can thrash any team in this event in any game because I have feeling most chances we will be having Manchester City, Bayern Munich or Real Madrid at the top with if any team can upset this is only Inter Milan all others are having no performance which is needed to be stood as champions of the Europe.