It's a Asus ROG and I immediately swapped out the 128GB SSD M.2 for the 500GB Samsung M.2.
With all my Visual Studio and such I have over 200GB free. If you go with the 256GB that will work too but you'll have to manage installs and where you store your files.
Me? I just want it to be easy. So I bought the Samsung M.2 card and moved up a notch.
I am customizing an HP Envy 15t. I am choosing between a 1tb 5400ram SATA with 256gb M.2 SSD or the 512gb PCle NVMe M.2 SSD. This will be my college laptop, which has to support my engineering programs on the laptop and support some movie streaming, and gaming.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic