The nexus 6p is guaranteed to get at least 3 years of updates, has a slightly better camera compared to the s7 (6p does not have optical stabilization, but does have digital), and has stock android (which would be easier for you to use coming from a moto g.
The S7 is nice if you want to buy into, and stay in, the Samsung ecosystem but does have touchwiz which will make the experience far different from the moto g (but it has gotten considerably better).
You really can't go wrong with either of these phones, all have great battery life. The only difference is features (which you may or may not use (lg g5's module exchange)). Bear in mind that the phones are considerably larger than the moto g, may or may not be a problem...