The general rule of thumb is if you work with files larger than 1GB, then purchase the Intel 750. If you work with files smaller than 1GB, then purchase the Samsung 950 Pro. The vast majority of consumers usually work with files smaller than 1GB.
Consumer feedback indicates the Intel 750 startup is slow. A few days ago Intel issued a firmware update to try an speed up startup.
The Samsung 950 Pro has not been released for sale yet so there are no technical reviews. However, Pure PC, which is a Polish web site published a review of a pre-production model. Here is a link to and English Language version of the review:
http://www.google.com/translate?langpair=pl%7Cen&u=http://www.purepc.pl/pamieci_masowe/samsung_ssd_950_pro_m2_test_superszybkiego_dysku_pcie_nvme
Translations are available in several other European Languages. Look for the small national flags at the top right of the web page.
I maintain an ssd database listed in a sticky at the very top of this forum section. Here is the link:
http://www.johnnylucky.org/data-storage/ssd-database.html
You'l find the Intel 750 and the Samsung 950 Pro listed at the top of the database. Follow the links to the technical reviews. I will add technical reviews of the 950 Pro as soon as they are published. The reviews are in English and many other languages.