Also, taking in account what others have said, (almost) all brands have inside, in fact, Toshiba NAND chips. Yes, the reliability of the case and the controller can make a difference
Isn't controller the most important part when it comes to write speed?
Hmmm.... well... yes and no. It depends. Theoretically all things being equal, yes, of course. But in our concrete case, generally no. (Ok, not so much).
Let me explain:
The cards are rated to 1000x, 600x, 400x aso. Hence their sustained data transfer rate must be somewhere around these values. Hence very different write improvements (like different arrangements of RAID-esque architectures etc.) will push-pull the card in another speed class. An exception here is SanDisk whichd doesn't obey to the standard rating of "NNNx" varies significantly the speed in the same line (eg. 'Extreme Pro' line) which indeed indicates that they use different controllers / data access strategies (for ex. stripping) or other enhancements in different edition of cards (it seems that 128 GB is the fastest and 64 GB is the slowest by a perceptible margin).
Also, another thing to note is that the main bottleneck (like in the case of computers) is, by far, the storage media, followed by the data access type (eg. RAID type - the number of stripes). Yes, the controllers can make a difference but not so much, and, also, bear in mind that in the card market isn't easy to enter, hence hardly one finds a 'cheap' solution with a 'bad' controller (except, of course, fake labels, as I mentioned in my earlier post).
