As of today, I'd say the Marshall trade is clearly the best. Getting an all-star starting pitcher for a reliever is definitely a win (no matter how good that reliever was).
On potential, I'm still holding out hope that Vizcaino gets healthy and we get a solid player out of that deal.
And while I like the deal, I wouldn't call the Rizzo-Cashner deal a win for the Cubs quite yet. Rizzo has shown some flaws and Cashner has pitched well at times (granted pitching at Petco helps that). I think it will favor the Cubs in the end, but not the slam dunk you might have thought a year ago.