What is the fastest micro sd card I can put in samsung galaxy S4?

[AC Question]

Which speed would give the best bang for the buck?

 

[STARGATE]

You can use either the red and silver or the Gold and red SanDisk. Those are the best bang for your buck.

 

[Rukbat]

The SanDisk Extreme is the fastest, but unless you're doing 4k video (and unless you have an 80" or larger TV, you'll never see the difference between 1080 and 4k), a U1 Ultra is fast enough. (As far as absolute speed goes, the card can't be too fast. As long as it's fast enough - and a U1 or Class 10 [same thing, different numbering systems] card is - you won't have a problem.