The interface type
SSDS can use NVMe or SATA as a way to communicate with the rest PCS. SATA is slower than the NVMe.
On the other hand, m. 2, in fact, a kind of overall dimensions. You can find outside NVMe m. 2 SSD and SATA m. 2 SSD.
Sometimes product advertising or using "m. 2 SSD" to suggest NVMe drives and "SATA SSD" to represent the shape size is 2.5 inch SSD. So don't these phrases on the surface. Instead, please see the technical specifications to determine a laptop or desktop computer storage roughly the speed of the drive.

speed
NVMe drive faster than SATA drives. (even if both the SSD with m. 2 dimension, too.)
Transfer rate depends on first your NVMe drive using which generation PCIe connector, and then is a single model.
At present, the NVMe PCIe 3.0 (aka Gen 3) SSD Max speed up to 3500 MB per second, while the NVMe PCIe SSD (also known as Gen 4) 4.0 up to 7500 MB per second. Manufacturers usually list the specific model theory of speed, and then you can check the independent benchmark results to verify.
SATA SSD usually at a speed of 500 MB per second. (but, like the NVME drives, various types of performance may be different.) This may sound is surprisingly slow, but compared with SATA hard disk, differences still like day and night - 7200 RPM hard drive in the top speed of about 160 MB per second. In the document editing or basic tasks such as web browsing, almost everyone noticed significant differences between the HDD and SATA SSD.
So why choose NVMe not SATA drive? When you load or copy files (especially when large files), become very obvious advantages.

The factors to
In a typical desktop computers, notebook computers and preloaded on NVMe SSD usually adopt m. 2 dimension. (there are other forms, but they are far less common.) SATA SSD can use 2.5 inches or m. 2 drive form.
If you have spare laptop m. 2 slot, please check whether support NVMe, SATA, or both, and then buy drives.

The price
As you might guess, the faster the drive, the more you pay the cost of. At present the market price of the 1 TB SATA SSD approximately $90 to $100, and recommend a type 1 TB NVMe PCIe drive around 3.0 in 115 to around $120. Is expected to buy 1 TB PCIe drives the price of 4.0 in 120 to $200, between you