Best answer: Right now the 128GB Samsung EVO Select microSD card is the best value in the lineup at only $29 with free Amazon Prime shipping, beating out the other two choices on the dollar per GB scale.
Amazon: Samsung Evo Select 128GB microSD Card ($29)
The 128GB card is the best value per gigabyte
As always with storage, the more capacity you want, the higher the price. Trying to cram 256GB on a piece of silicone the size of your thumb requires more technology and more money so the cost is higher when you look at the dollar per GB scale. You can get two 128GB for only $58 or one 256GB EVO Select for $72. That's a difference of $0.22 per GB and $0.28 per GB respectively, which may seem like a small amount but if you are looking to buy multiple cards that difference soon stacks up.
When it comes down to the question of value, monetary value plays a huge part, and buying two 128GB microsSD cards is a significant saving over the 256GB model.
The cards themselves nearly identical
Except for the price, the Samsung EVO Select 128GB microSD Card and the 256GB model are exactly the same. Both have speeds of up to 100MB/s read and 90MB/s write and both are UHS-1 Class 10. There is a caveat that if your device isn't running the UHS-1 interface then those speeds will be lower but the cards themselves remain tied for speed regardless of their capacity. While real-world tests show you are more likely to get 80MB/s or even lower, there is no discernable difference in the speeds of the three cards.
The only real difference in the cards is their operating temperatures. The 64GB Evo Select and the 128GB will operate between -13 and 185 degrees Fahrenheit while the 256GB can operate between -25 and 185 degrees. So if you are spending a lot of time out in the cold, the 256GB may be one to consider.
Two cards are better than one
When thinking about the value of a microSD card, you also have to consider how you are going to use it. Having two 128GB cards gives you a lot more choice on how you use your capacity. In a camera, for example, you may want to split your cards for different projects or in my case, have separate cards for separate 3D printers rather than transferring the data between them. You also get the full SD adapter in the packaging giving you even more ways to use the two cards effectively.
While a 256GB EVO Select microSD card sounds like a great thing to have, and big numbers are always cool when it comes to storage, having a choice with what you can do with that much storage is far more helpful.
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