Vucinic's stats are not any better....stats aside, both players probably are not good enough subs for us they both don't make a great impact. quags has been more decisive over the years with his goals in the CL...Vucinic played important roles in serie A and helped us win important games. Either way, both should be leaving.
And yes, I'd still take Quags over Vucinic...may be just me who thinks this but Quags works harder, has a better finish, can create and score...Vucinic can do some fancy stuff and look very good on his day but it is far and in between.
Im sure both would be a success at their next club if given starting roles.