I suppose I'd say the biggest wildcard is Vazquez's bat. If it comes around as some people think it will, and as I think it will, he's an everyday guy, no questions asked. He's already major-league ready as a backup or even as a light platoon, but as long as the hitting is in development, you wouldn't want to expose him. If the bat does come, and let's say something like .255/.335/.400 is not an outlandish ceiling for him, he's going to catch 120 games a year and be a core up-the-middle player. To me, the major reason to keep him in Pawtucket is just that -- to see if he can develop offensively to the point of being an everyday guy.
Swihart is not nearly as advanced as Vazquez defensively, which is to be expected considering he is learning it on the job, but I also don't think he will ever profile at Vazquez's defensive ceiling. There are some things, particularly pitch-blocking, that he might eventually do better because the athleticism is real -- not just good for a catcher, but in some areas high-caliber for a big leaguer. His bat will be better and more valuable because it's a switch, and it will be better, I think, than even a lot of the people really high on him think. It's a tough deal to learn how to hit professionally, and to do it while switching, and while learning the most demanding position on the field, is an even greater challenge. And yet he's doing it, which suggests to me something special when it all comes together. I think it will be more than good enough to carry a position switch if that becomes necessary.
I guess the short takeaway is Swihart is an elite athlete making greater progress than even his excellent stats suggest, and Vazquez is already an elite defensive catcher with a chance to be an everyday player. Swihart is number 1 for me because he has the highest offensive celling, and because of his positional versatility.