Welcome to Android Central! Yeah, I'd stay away from the no-name generic ones. If they do work, they might not last that long. Stick with known brands like Sandisk, Toshiba, Samsung, etc. And buy them from reputable sellers, like big name stores or directly through Amazon (not through the Amazon Marketplace). When you get it, you can run
SD Insight to make sure the card is what it says it is, and not counterfeit.
I think the S3 allows you to move portions of an app to external SD, but you can't move the entire app over--a good amount of it needs to remain in Internal Storage. You should use the external SD primarily for media storage.