As of July 2014, the availability of Samsung Galaxy S5 Compatible 128GB microSD cards is quite low. What I have noticed is that people are simply recycling some of the 128GB microSD cards by buying them low and attempting to sell them high. After searching several sites, I recommend sticking to Amazon and purchasing one with a good user rating. There are knock-offs out there and also some that have been formatted for other devices and may not work on the Samsung Galaxy S5.
If you purchase a knock-off 128 GB microSD card, you run the risk of complete incompatibility or even worse, the loss of your data after you have stored valuable pictures, music, videos, and other files. Not all incompatible cards fail right away.
Purchase from a reliable vendor with good customer feedback meaning multiple people have made a purchase of this particular card and are satisfied. A reliable and compatible Samsung Galaxy S5 128GB microSD card is the SanDisk Ultra 128 GB microSDXC but be prepared for a waiting list as of 4/13/14.
Compatible Samsung Galaxy S5 Micro SD Cards
Compatible Micro SD Cards
|SanDisk Ultra 128 GB microSDXC||128 GB||48/<30 MB/sec|
|Samsung Electronics 64GB PRO Micro SDXC||64 GB||90/50 MB/sec|
|SanDisk Extreme Plus||64 GB||80/50 MB/sec|
|Samsung Pro microSDXC Extreme Speed||64 GB||70/20 MB/sec|
|Samsung High Speed microSDHC||32 GB||24/13 MB/sec|
|Samsung Plus microSDHC||16 GB||48/23 MB/sec|