What is more important to you, hardware or software?
If you want the very latest hardware and you don't care about bloatware and really slow software updates get the S7, it has an 820 CPU, OIS and wireless charging, the 6P has an 810 CPU, no OIS and no wireless charging although it does have a big screen and the S7 has a small screen.
If you want the latest version of Android, no bloatware and no carrier interference on the software updates (I'm looking at you Verizon), get the Nexus 6P. Everybody is very happy with the 6Ps hardware so there isn't a lot you would be giving up with the exception of wireless charging which is the one important thing they left off of the 6P. The alpha of Android N came out this week, only the bravest of souls are running it but you could if you wanted to, by this summer there wiil be a stable release of N for the 6P. Samsung won't roll out N for the S7 until next year, and they may never roll it out for the S6.