Ok so - played ED in both the Rift and Vive tonight - here's the observations.
Vive was first up:
The Vive was a Pain In the "bottom" to set up. Still not liking the comfort, but anyway - into SteamVR, launch ED, and then I'm back at Vive Home, then I get some flashes, the loading video, and I'm back at Vive Home again. I tried everything I could to get it to work, but it took 6 attempts with reboots etc. Again, the Audio didn't swap, but I've found the setting in SteamVR which does that so it should in future (I hope). Once I finally got it to work, it was poor. DK2 resolution pretty much - but that's a known issue. Godrays weren't too bad, and not noticeable for lag, but the res and text weren't as good as I was expecting. Popped the res down to VR LOW and that was a bit better but still DK2 or worse. Meh.
The the Rift:
First time I started ED from SteamVR it dropped me into Vive Home, rather than Rift Home, but I guess that's just because I have both. Restarted Steam, and hey presto, no problems.
I've been wearing the Vive all day trying to get the thing comfy and to work better, and I was unprepared for how easy the Rift is to put on (think headphones),and how comfy it is. Straight into ED via Oculus Home - no issues. Text is perfectly readable. Godrays are ok, went to the settings menu and upped it to VR High as I was feeling confident.
Launched into my alt account which was sitting in an Eagle in a station in Leesti.... And that's when I lost my (insert descriptive word here).... It is AMAZING.
Even with the DK2, I've never really gotten the scale of ships and stations, until now. The Rift did it in a way the Vive did not - I think due to the res bug mostly, but it was, even as someone who has played with a DK1 & 2 before, epic - the Rift made it so much more visceral.
So much so that I got out of my seat to inspect the corridor behind me and look out the upper windows at the docking port (leaving my headless corpse in the seat!). The Rift isn't just a seated experience btw. I only have about 1m x 2m travel max but that was enough to get up and wander around the cockpit.
TL: DR - the Rift is (and I stress imho) the best device for ED currently. If FD fix the bug with the Vive, there'll be little to choose between them I would guess on image quality (although the Rift seemed smoother - again, bug?). After they fix that it'll come down to ergonomics, and it's difficult to explain how far the Rift is ahead of the Vive here unless you've owned a DK1/DK2. The Vive is a DK2 on steroids with the DK1's cable management, and lighthouses - the room scale is cool, and I look forward to getting enough space to try that properly, but for me the Vive is very uncomfortable, the cable is too thick and heavy, there's too many cables to setup/manage, and the lack of built in headphones is a major issue.