3rd party drive or standard in a new MBP?
For something like this, I would always buy my own and put it in for two reasons:


cost
you get an extra drive to play with


You will find better deals on SSDs if you purchase your own. However, there is one reason you would want to go with the Apple-supplied drive:


TRIM support


That's about it. I guess, if you know and value what TRIM support is, you only have one choice. If you are fine putting in your own drive and don't value TRIM support, then you have other options.