It's pretty hard to stop eating the Google candy. It's just they're generally pretty fantastic at software. We know all too well that terrible software litters the world around every turn. So when I pitted a OnePlus 5 against a Pixel XL, the Pixel's superior software and updates made the decision pretty clear. It was a serious bummer, however, because the OnePlus' hardware felt much better than the Pixel's. I wanted the two phones to have a kid with the best parts of each.
Speed and price
Getting into it, both of these phones can be had for somewhere between $400-450 used on Swappa. Just keep an eye on the postings and jump on the deals! Although the guts of the OnePlus 5 are newer and faster, both phones totally scream and I found that I was almost never waiting for anything. The fingerprint on the OnePlus, however, is a tiny bit faster to unlock than the Pixel.
Holding the pixel feels like holding a flat empty box, whereas the OnePlus feels like a solid brick. One can make arguments for either camp. I found that I preferred the solid brick.
The power button feels loose on the OnePlus, while all buttons on the Pixel feel solid and clicky. The OnePlus actually innovates and introduces an extra 3-way switch that toggles between silent/do not disturb/sound on. Finally, the OnePlus' front fingerprint blows the rear Pixel fingerprint out of the water. Hands down, the OnePlus' hardware is gorgeous and is much preferable to the Pixel.
Charging & Battery Life
None of my USB-C chargers for my Nexus 5X work for fast ("Dash") charging on the OnePlus. They do continue to work on the Pixel, including my aftermarket car charger. Special cable & charger for the OnePlus -- booooo.
I planned to buy an extended battery for the Pixel, but I'm changing my mind as the battery life is huge upgrade from my 5X. On the OnePlus too -- both phones were above 75% well into afternoon. Wow!
The real gotchas
The Pixel camera is better than the OnePlus. However, in my experience, both cameras produced absolutely high quality photos, and were fast and responsive. So unless you're a total photography buff, don't let this make or break your decision.
Video recording is another story. The video stabilization on the Pixel, while recording, is absolutely the most unbelievable stabilization I've ever seen. Make sure to try it out if you go to a store to hold a Pixel. The OnePlus has none of it. However, I don't do much video on my phone, so not a big deal for me.
I also noticed the OnePlus jelly scrolling issue, but found it purely visual and did not impact usability.
Google Fi on the OnePlus works fine after activating on a Google device. The Project Fi app at first did not work, but after a day or two, suddenly started working and hasn't stopped to this day. The Fi app's wonkiness had nothing to do with whether the phone had service -- no problems there.
Now, the biggest gotchas
I noticed some popping while playing music via Google Music at the beginning of songs on the OnePlus. Not always, but fairly annoying. A restart temporarily fixed it.
However Google Music really doesn't like the OnePlus, because I am unable to scrub at all, it always just resets to the beginning of the song. Some Google research indicates many have the problem and OnePlus blames Google for it. The Pixel does not have this issue at all. This is kind of a showstopper for me.
EDIT Aug 31 2017 - OnePlus has rolled out a fix, woo hoo! Crisis averted.
Despite my attempts, the OnePlus doesn't seem to support waking the phone up with OK Google. So if you're hoping for an always-listening Google assistant, you'll have to stick with the Pixel.
In conclusion, we live in an extravagant period of time where everyone you see on the street is holding a miracle in their hand. In my opinion, both of these devices are the creme of the crop right now and you'll be very happy with either. However, the Pixel does have the edge.