I think Daniele De Rossi will be talked about well in Europe, it's still too early to tell but I think Roma can fight to get at least to the semi-finals. Of the three teams I've chosen, I think Porto are the most dangerous and as you said, they are tough to beat, and you know that in the Champions League too. Manchester United always start badly lately but then they bounce back, we'll see what they are made of this year.
Roma has been a regular appearance in the Europa in recent times and they have continually made sure to keep up with the struggle to getting the Europa trophy some day, I believe that has influenced the almost frequent change of coach within a very short period of time but importantly is the fact that they have been able to keep their focus on the game and I believe this season they will make better advancement than they had done in previous seasons where they weren't able to get a chance at the trophy, last season was one of the closest they have gone and we are hopeful with Rossi they will do better because since his arrival a lot has changed with Roma and they are appearing like they will do better than they had done last season.
AS Roma is having last two seasons good at the Europa Cup with once lost in semifinal and then in final things are surely perfect for them to have good results but their start in Serie A is not ideal because after having draw against Cagliari they lost at home against Empoli with De Rossi is surely having some pressure after having good end in last season things are looking not as they needed for the start of their campaign in this season.
Even now in last few years we have good development for the Italian clubs but still they need to work out on their quality because things are getting challenging after every season so they have to compete with these otherwise they could be going down and out of the race like we have Italian national team from the World Cups in last few years now Roma is going to visit Turin for the challenge against Juventus which is doing good in this season as well.