Its a matter of which annoys you the least
DK2:
Dev kit, that may or may work for much longer, all depends on the FB/Oculus people and how long they will keep their software running with it.
Fairly heavy, long sessions will lead to some neck/back pains (it does for me, I am getting old).
SDE is very prominent but you learn to tune it out.
Works flawlessly on 970 in ED right now, I know I have one of those (although recently upgraded to 980ti).
Lenses don't have god rays, but have chromatic abboration which can be quite noticeable at times.
Some people have really bad smearing, personally don't have it with latest Nvidia drivers.
CV1:
Current officially support HDM by Oculus. Higher resolution than DK2, higher required frame rate (90 vs 75).
Great ergonomics, much lighter than DK2 and Vive.
Works flawlessly on 970 if you can live with dialing down some settings.
SDE not 100% gone, but 95% of the way there.
Apparently has noticeable god rays due to using fresnel lenses. Fresnel lenses are lighter and eliminate the chromatic abboration.
Perfectly supported in ED.
Smearing is mostly gone.
Huge wait time on it, August+ when you order now.
Vive:
Same resolution as CV1, with same frame rate requirements.
Need to use steam vr to run ED with it.
Decent ergonomics, lighter than DK2, heavier than CV1, more balanced than DK2 but apparently can still cause fatigue issues.
Due to steam vr not having ATW (Asynchronous TimeWarp) needs something beefier than a 970 to be use-able.
Currently a bug in how Vive and ED interact that is causing terrible aliasing and graphics issues, its being worked on (don't believe all the doom sayers, I am sure they will work it out, just like with the oculus runtime).
Uses different fresnel lenses, but still has god rays, some people say they are less than CV1.
Has room scale which CV1 does not, but for ED that is irrelevant (for now).
People are reporting more production issues with Vive than CV1 (dead pixels and things of that nature).
More expensive than CV1 due to extra controllers, once oculus has controllers too price will be the sameish.
SDE almost gone too, apparently slightly more notice-able than CV1, but don't take my word for it.
That is about it I think, I probably forgot something that people will correct me on I am sure.