I'd take Zubrus - he's younger and bigger and seems like he's finally playing as well as the Flyers had hoped. Prospal would not be as successful here as he is in Tampa - unless he played with Forsberg.
Zubrus was always so overrated in the time he was here. Being big, fast, and having one spin move that never worked anyway (not to mention the ladies liked him) got him much more play here than he should have ever had based on his actual merits.
He's an underachieving 2nd line forward. Has been his entire career.
Now, Vinnie has at least a few things to like about his game. He is skilled. He has a mean streak - not to mention he does the same thing Joni does - goofily smile at people while he's pissing them off. He's a good 2nd line player who has had 1st line moments. If his skating was any good he'd really be something.
It depends what kind of role you want them to play. Vinny is obviously more offensive and puts up more points, but Zubie has turned into a good two-way player. He plays very well defensively on the penalty kill and often is assigned to check the opposing teams' big power forwards. He never developed the offensive skills that everyone thought he had, but he does the little things well. He's playing with Ovechkin this season because they have chemistry but ideally he's more of a second or third line centre.