If I had both phones in front of me, and had to pay for one or the other, I would go with the HTC. The size, processor, etc.
BUT....if I hadn't been forced to part with my beloved Nexus 6p, I wouldn't be a debate. Keeping the 6p would be that cheaper option (I assume), and we are both waiting for the HTC Nexus.
Now, here is an interesting idea. The HTC 10 might be very similar to the HTC Nexus. It might have a different screen size, as well as other difference....but it might be closer to the HTC 10 then it isn't. If HTC really does role out fast updates (I expect updates for the unlocked version to follow close behind the nexus line, especially with them making the next nexus), and the phones are similar enough, along with HTC's uh oh protection....will it be worth it to move from the 10 to the HTC Nexus? Could be an interesting predicament.
I'm loving the 10. Zero regrets.
As a side note, for you HTC 10 owners:
My HTC 10 hates the Pixel C charger
http://www.androidcentral.com/my-htc-10-hates-pixel-c-charger
So yeah, be careful. People seem to want to blame HTC, which I believe HTC deserves some blame; but so does Qualcomm. USB C is still new enough to have compatibility problems, and proprietary technologies like quick charge appear to have some conflicting protocols or lingering incompatiblies.
I think this will get worse before it gets better. I imagine the first Samsung phone with USB C, possibly the note 6, will use a its own fast charge technology that may conflict.
So essentially until it's all resolved, stick with OEM made chargers, or reputable quick charge brands (and monitor it the first time). I imagine most quick charge chargers will be fine, since the voltage is low enough (amp can be oscillated on demand, voltage is constant). But USB C chargers, such as a MacBook or pixel C charge may be too powerful.
I'm not fully sure what the main problem is. I know a pixel C charge can charge a nexus 6p fine...but it almost fried a HTC 10. I think we have a conflict between the quick charge technology, and the large amount of power some USB C chargers can output.
So just be aware. I have used a quick charge 2.0 wall and car charge from Amazon, as well as a Samsung fast charge plug with the HTC ten without a problem.