[Google Pixel XL Accessories] hokiealumnus:
Ok, I'm trying this again now that I've made it to a PC to post...

Well, I have finally found my Holy Grail of a case. It only took four tries, heh. Below are my findings, in order from least favorite to most, and why.

Tudia Arch Matte TPU (in Blue)

I really want to like this case. It has a great in-hand feel, and the button 'clickiness' is the second best of the three cases with button covers. Unfortunately it was just too slippery for such a big phone and my hands.

Pros: It would likely protect the phone from decent falls, there is a lip to protect the screen, it feels nice in the hand, it looks great.

Cons: Too slippery. It turns my mostly one-handed operation of the Pixel XL into mostly two-handed.

Nillkin Nature (in Clear)

This is almost certainly -the- thinnest case you will ever find for the Pixel XL, outside of D-brand (or other brand) skins. It's comfortable, but offers basically no protection outside scratch protection.

Pros: Great fit, super thin, the clear model shows off the Pixel XL as it is meant to be seen, comfortable, not slippery at all.

Cons: Very close to zero protection for drops. Button feel is mushy; it ruined the excellent clicky buttons on the Pixel XL for me. Just yuck on button feel. The USB-C cutout was also a little too small, and caused my data cable to be wonky unless I pulled it off. There is also no taper at the fingerprint sensor - necessarily, because it's so thin. But there is an edge there that is a minor annoyance.

Bear Motion (in Blue)

This is the least "case" of all the cases. The top & bottom of the phone are completely exposed, as are the aforementioned excellently clickly Pixel/XL buttons. I love the way this "case" feels, but the "protection"...

Pros: Great fit. Open buttons. No interference with...well, anything. It's basically an added grip accessory for a slippery phone. Speaking of grip, this has a nice texture and is non-slip.

Cons: No. Protection. At. All. It doesn't cover the top and bottom of the phone, which would be fine if it at least made it all the way around the corners. It doesn't. I lived in constant fear of dropping and denting/scratching/breaking my phone, even though I'm already careful. If it went around the corners a little farther, I'd be much less worried...but it doesn't. The lip going over the screen edges is also weird - it gets deeper as you go down the phone, as though they didn't properly measure the Pixel XL's taper. That last one is minimal though, and isn't too bothersome.

Caseology Waterfall (in Ultra Clear)

The Caseology case is the holy grail. It has decent protection (none of these is going to be an OtterBox), and the corners have internally reinforced TPU to help with drops.

Pros: Great fit. No interference with ports at all, the cutouts are perfect. The button feel is superb - the buttons are covered, but they feel just as clicky and responsive as if they weren't. It looks like they thinned out the TPU (inside) around the buttons to accomplish this, and it's downright perfect.There's a nice lip around the screen if you want to put it face down. It's just as non-slip as the Nature, but actually protects the phone. Oh, and like the Nature it also shows off the beautiful phone underneath.

Cons: None. Really, none. It does get some pocket lint around the edges, but so does every TPU case I've ever tried, including both of the ones above. It's just more noticeable with this one and the Nature, because they're clear.

The only thing I can't speak to is the Nature's & Waterfall's ability to STAY clear. There are reviews on both that mention yellowing over time, but not very many. I'm guessing this has more to do with particular users' environments than anything else (i.e. smokers, people that use their devices outside a lot, leave them in the sun, etc).

There you have it! I intentionally didn't link to them because I don't want to appear to sponsor one site over another. You can see photos of the phone with the Tudia & Nilkken cases here. I have only had the Bear Motion & Caseology ones a couple days and haven't had the chance to take photos of them.

Verdict: The Caseology Waterfall is the one that will probably stay on my phone from here out, occasionally switching it out with Bear Motion. If I had 100% confidence in my ability to never drop my phone, I'd probably use Bear Motion all the time instead.

If you have questions, feel free to ask. This thread helped me a lot when choosing good, thin(ish) cases, so thanks to those that came before!