To start with, they're both fantastic devices. I doubt that you'll be disappointed in either of them unless you're looking for some very specific things. I've seen so much obsessing over field of view and pixel density and other crap recently. News flash: you won't care. You'll put on the headset of your choice and say "Aw... this field of view isn't what I was hoping for! And look, I can totally see pixels if I stare hard enough!" and then the content will actually start up and you will probably never think about it again. Do I want these things to improve in subsequent hardware generations? Sure! Is it a problem for this generation? Not in the slightest.
More meaningful is the difference in the industrial design and ergonomics. The Vive is a overall a comfortable device to use, but it takes a bit of fiddling with the straps to get it so it's not sitting on your face uncomfortably. Even once it's on it feels a little front heavy. It's not bad, really, and the only reason I bring it up at all is because the Rift is fantastically comfortable. The rigid straps allow you to easily get it on in exactly the right way so that the weight is primarily on the top strap, the back of your head, and your forehead. It feels like wearing a large hat, rather than goggles. The Rift is also undeniably a sexier piece of hardware. I think the Vive actually looks fine, but next to the Rift it seems like a really polished dev kit.
The exception on the ergonomics front is glasses: I can use my glasses with both headsets and while it's not perfect it's not annoyingly uncomfortable either. When I take off both headsets my glasses usually come off with them, so I have to pull them out from the facial interface. On the Vive it's no big deal but the Rift holds onto my frames for dear life. It's seriously hard to extract them from the facial interface without feeling like I'm damaging something. :( My glasses are pretty wide (146mm), so your mileage may vary, but it does make me wonder why Oculus didn't follow through on the idea of including multiple facial interfaces.
The headphones also make a big difference. I have nice headphones. I like to use them whenever possible. But I'm super glad that the Rift has integrated headphones because it's one less thing to worry about when moving in and out of VR. It's a small thing, but fumbling around for headphones after you've got the headset on, managing the extra wire coming off the back of your head, and remembering to take things off in the right order is just enough of a pain to make integrated audio extremely welcome. (And it doesn't hurt that they sound pretty good too!) The camera on the Vive does make up for it a bit, and it's clearly a feature that would improve the Rift. It's honestly a bit odd that they left a camera out after having the pass-through was such a well regarded feature for the GearVR.
Oh, and I can't forget to mention how much easier the Rift is to set up. The Vive set up process is nothing terrible, there's just a fair amount of stuff to deal with. Base stations, controllers, breakout boxes, wires everywhere... I've taken mine back and forth from my home to my office multiple times and each time setup or teardown is about 20-30 min. And that's with experience doing it! If you're not planning on moving your VR setup around like I do, though, it's a complete non-issue. The Rift, by contrast, is super fast to set up and tear down and has a really nice carrying case to boot! I suspect that you'll see a lot more Rift's than Vive's at various meetups, conferences, and hackathons simply because it's easier to transport and set up.
This level of hardware polish extends to the Rift's upcoming hand tracking controllers as well. The Vive controllers are great! No real complaints to be had. They feel good in the hand, are super responsive, and extremely intuitive. In the brief chance I had to play with Oculus Touch, however, I found it to be more comfortable to hold, lighter, and the triggers to be easier to use (especially the grip trigger.) And that was just a prototype! I'm sure the final consumer release will be even better... whenever that actually happens.
(Fanboy trigger warning: This is the part where things stop being so glowingly positive for the Rift.)
See, here's the problem: I've shown a lot of people the Vive and the Rift. Every single one of them has been blown away by the Vive. People who were complete VR skeptics have walked away going "Wow, I need to find some space in my house." On the flip side, when I show people the Rift (usually not the same people I've shown the Vive to) I place the Oculus Remote in their hands to navigate and every. single. one. of them immediately waves it in front of their face and frowns in disappointment. They watch some demos or play a game and walk away saying how impressive it is, but almost everyone makes a remark about how they wish they had hands. Similarly everyone that tries the Vive is delighted that they can walk around, while everyone trying the Rift comments about how they're scared to move for fear of smacking into something.
As it exists today, VR on the Rift is "really impressive" and VR on the Vive is "OMG this is incredible!" and it comes down to tracked hands and Chaperone. When you feel safe walking around a space and can actually reach into it with your hands it's an entirely different level of immersion. That's not to say the Rift isn't good at what it does. Lucky's Tale is great fun, and anything that sticks you in a cockpit is a wonderful fit for the device. But when I think about my favorite experiences in VR to date it's shooting down drones in Space Pirate Trainer, building crazy vehicles in Fantastic Contraption, painting with light in Tilt brush, or doing whatever you do in Audioshield. (Rhythm boxing? Musical defense? Audio deflection?) None of that is possible on the Rift today, and I feel it's absence intensely.
The good news is that it's hopefully a temporary problem. Touch is coming, and I have every expectation that it will be fantastic. And if Oculus doesn't provide some sort of Chaperone system when Touch is launched they've screwed up big time. I can't imagine that they won't. Even then, though, some problems will remain: It's harder to set up the constellation sensors in a configuration that minimizes occlusion and it's not clear what percentage of the user base will pick up Touch, which may make it a less attractive development target. I really hope that people do, because it makes a world of difference, and I would like nothing better than for VR with tracked hands at room scale to be the effective baseline for desktop VR.
Looking beyond the hardware, I feel that Valve's software is simply more mature than Oculus'. Sure, Oculus Home is a gorgeous environment, much nicer than SteamVR's photosphere. But why does the entire store need to launch every time I start a VR app? And why does the Oculus Store window pop up over the top of whatever I'm doing if something happens to trigger the proximity sensor? Features like friends lists are pretty sparse in their functionality, the lack of any text input in the Home environment is frustrating, and it has weird bugs like rendering that beautiful home in the background even when you're not using the headset. On the other hand SteamVR on the other hand is, well, Steam! While the VR variant still has some quirks it's basically the same system you know and love with some new tricks. The theatre that I can play 2D games in is great, even if it's not a pretty environment, and having basic desktop usage that you can call up at any time is a life saver. Especially for development!
(And I have bigger complaints on the development front, but that's probably material for another post.)
Again, this is all fixable on Oculus' part. There's no fundamentally unsolvable issues here, and I'm hoping that in 6 months time most of this post is obsolete. But it as of today the Vive feels like a more complete hardware and software package, even if Oculus wins on aesthetics.
The most important takeaway, in the end, is that the current gen of VR is compelling no matter which hardware you experience it with. Nobody is poisoning any wells. Both devices have their pros and cons, but neither are bad by any stretch of the imagination. If I could put together a dream system it would probably be a Rift+Touch, tracked by Lighthouse sensors and using SteamVR. Back here in the real world, though, I think the Vive is going to stay plugged into my PC a lot more than the Rift for the time being.