Well OP, I haven't used the Pixel XL but I did use the S7 edge (and the Note 7), and it really boils down to this.
You go with the Pixel XL if you want;
- Fast and timely updates direct from Google
- Want a USB-C port
- Prefer Google's own vision of Android
- Want the absolute latest and greatest hardware wise
- Want something different
On the other hand, you may fancy the S7 edge if;
- You want everything but the kitchen sink in terms of features
- You also want a phone that looks pretty (subjective)
- You want water-resistance
- You need an SD card slot
- Samsung Pay
Personally, I'd take the S7 edge. I really liked that phone and personally, I think it's still probably the best all-rounder of 2016. Of course, this is all subjective, but my best advice is to give both a test drive and see which one best fits your usage.