the MBP's use MLC chips.. Pre Mid 2015 they used Toshiba MLC NAND for I think just the 128GB drive, and Samsung for the larger.
Now where it gets interesting, the insane nearly 2GB/s updated SSD in the Mid 2015, if you look up tear down pics, and look up the chip part numbers, they are the same chips that are on the new Samsung 950 Pro which didn't come out til 6 months later. So My guess is the Mid 2015 basically has an Samsung 950 Pro M.2 PCI-E SSD