micro sd card -whats the best and largest

The fastest would be any Class 10 card. It looks like the Galaxy S3 supports any sizes available, including 64 GB, which is the largest I've seen. I've heard of some 128 GB cards coming out soon, which I assume will also be supported.
 
The GS3 supports 64gb. You can get a dongle USB adapter and plug the 128 into that with a flash drive adapter.

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Never had an iphone, and don't want one. Tapatalk on Samsung GS3.