In my (anecdotal) experiences with SSDs:
- regarding read/write speeds: Sandisk is good, Samsung is better.
- regarding price: Sandisk is very reasonable priced, Samsung charges quite a lot more.
- regarding longevity: Barely a difference between Sandisk or Samsung.
So, if speed with read/write is of the essence, get the more expensive Samsung drives or the really expensive Intel drives. Those are top class and charge you for it. Rest assured though, compared with a standard hard disk, any SSD drive (SATA models or NVMe models) will be a huge step faster. And you will not want to go back ever again.
This part is only something to consider if you are handy with electronics and your laptop comes with a DVD/BluRay device. Now, I do not own a laptop myself, else I would have attempted it, but I have seen blogs where people were successful in removing the DVD/BluRay device from the laptop and reuse the bracket to mount a second SSD drive in their laptops. With some it also took some electric rigging to get the power supply and data lines from the DVD/BluRay device to connect properly with the second SSD.
How much rigging is needed depends on the type of SATA connector in the laptop from the DVD/BluRay device, the distance and orientation of the second SSD from that connector. That way you can get even more speed out of your laptop.
But again, this is only for people handy with electronics and don't mind about bricking a laptop if they make a (unintentional) mistake. Even if you do manage to make it work, you can kiss any guarantee goodbye, no matter what.