For Barcelona, I would take Arda over Vidal. You can't say Vidal is a "better player, plain and simple". They're different kinds of players. Kinda like how Rakitic is infinitely better for Barcelona than Fabregas ever was.
Thats an overstatement, Rakitic is no doubt a good player, but he hasnt really done anything special to be hailed as a wc midfielder. Right place at the right time, simply. Cesc didnt do as well as he should have, but Barca would have won the treble anyway, with or without Cesc.