I own a Zero SR/F, my second zero.
Just test drove a Livewire. Nice motorcycle!
In case you are interested, some observations:
The HD is even smoother than the zero (which is very smooth), with almost no belt whine and zero vibration. When in drive mode but not moving the HD sends a mild haptic pulse through the seat to remind you it's live (instead of potato potato potato).
Both are crazy powerful with good throttle feel. The HD felt a bit smoother but that's subjective. Both get an A+.
The HD trail is longer and the rake is the same, so the HD should handle better at high speed and the Zero better at low speed, but it felt the opposite to me.
HD bars were more comfortable for me. I just don't get the Zero sweep. YMMV of course.
Riding positions were similar. Felt a little less stretched out on the HD.
Regenerative charging with braking is goofy on the Zero (full on or full off, not progressive like in a hybrid car, and delayed on and off after brake lever action). I'm not sure if the HD even has brake regen charging.
The HD does have regen charging when coasting, fully adjustable just like a zero. Both can be set to match the ice engine braking of your preference. The HD activates the brake light when slowing with regen, smart.
(FWIW the actual effectiveness of both types of regenerative charging on my two Zeroes has been minimal, even when riding in the mountains. Kinda disappointing. Only the rear wheel contributes, maybe that's the issue.)
HD has Brembos. Zero has J Juans. Both work great.
Did not dive into suspension adjustments, sorry don't know. Factory settings were much plusher on the HD. Zero made more a track bike.
The HD is heavier, but did not notice.
HD seat was more comfortable for me.
HD has almost no built in storage and no available rack for adding a tail case. They may or may not offer a rack in the future. The passenger seat is narrow and short, would be hard to strap stuff on behind the rider. So that means a backpack for hauling and no real lockable storage. That's a huge minus for a commuter.
The Zero has a usb port in the frunk.
No frunk on the HD does make the fake tank area a lot narrower. This might enhance rider comfort, but YMMV.
Rearview mirrors on the Zero mostly show your shoulders and upper arms. You can't see what's directly behind. Rearview mirrors on the HD show your hands and wrists. Worthless.
The Zero has grip heaters that work very well for me. The livewire does not have grip heaters. They may offer them in the future. Unknown if a retrofit will be an option.
The Zero display screen seems to be a tad bigger and a bit easier to read. The HD's is still very good, and it has bluetooth that can work with your cell phone for GPS or playing music.
The Zero app is a minor PITA, but it works. Don't know about the HD interface.
Styling is a personal thing. I like them both. The Zero paint looks much better live than it looks on the website. The HD looks much better overall to me live than on their website. The phallic engine thing is much more subdued live.
Everyone knows the charging and price differences.
There are way more HD dealers, but most don't carry the livewire at present. Evidently HD requires a large commitment of time and money from a dealer before they can carry this moto. But if it catches on more, and more CCS/SAE level 3 charge stations go online, that would mean many more fast charging options, which might make 300+ miles/day practical, in contrast with Zero at present. Personally, I would be uncomfortable riding either for that many hours due to the rider position, but I think the HD would be more comfy for a long day.
Zero uses a key, HD a fob.