From reading the message boards and listening on the radio, there is almost universal agreement that going for two was the right call. I'd say it's at least 90%.
As for the QBs, I personally think Miller is clearly better. It's hard to judge because he has so much more to work with, but I think the difference is the bad decision making that is definitely a pattern with Gardner. The bad decisions are exacerbated by the porous offensive line, but they are ever present.