I think as long as it's class 10, you don't need to worry past that. Maybe some minor variation between brands, but I know I used G.Skill, Sandisk and one other brand (kingston i think) 32gb cards in my s3 to watch 720p videos and there wasn't a single one that stood out as faster than the others, they all played pretty much instantly and there weren't any issues.
Was thinking that the 16 gig plus msd would make this a supetphone but now have been reading that the msd can only be used for certain things nothing to do with google not apps, not games, seems only thinga like video shot with the phone and some pictures can go into the msd rest demands the on phone space. Wow not sure what to think of this.
Seen some articles on the web in regards to this.
Does your s3 inforce only certain things go into your sd card?
You are correct. Android only allows apps to be installed on the phones internal memory. However the SD card can be used for taking pictures, recording video, storing music and movies, downloading etc. The onboard camera isn't fast enough that the performance between different class 10 cards will be noticeable.