I'm on the fence about voting to close this question, because it's on the edge of being too broad but it's not explicitly too broad. I might as well post a partial answer, though, because I know a bit about Astronomy and might be able to contribute something.
TL;DR: Why would we terraform them in the first place? Go with Gliese 667 Cc.
I think the answer depends not on what the planet candidates are like but what the Earth is like. In other words - how desperate are we to get off the planet? Why are we leaving? Who are we sending? And will there be an in-flight movie?
Seriously, though. Let's compare the two planets.
Gliese 832 c
- 16 light-years away
- ESI of 0.81
- 5.4 Earth masses (a super-Earth)
- Temperature varies from 233 K to 280 K
- Has a sibling planet, Gliese 832 b
- In the star's habitable zone
- Orbiting a red dwarf
- Orbital period of 36 days
- High eccentricity - occasionally comes close to leaving the habitable zone (I think this graphic can show you how big a problem this could be):
Gliese 667 Cc
I have to say, I think this is a tough choice, but I would choose one of the two. Go for Gliese 667 Cc. While both planets have high eccentricities (Gliese 832 c has an eccentricity of .180, while Gliese 667 Cc has an eccentricity of 0.27), GLiese 832 c may occasionally stray out of the habitable zone. Gliese 667 Cc also is lower in mass, which is better for any settlers that would have to adapt after a long journey in microgravity - unless we go for artificial gravity. It could also have liquid water, which would be a huge plus. Sure, it's further away, but if we're willing to go 16 light-years out, we might as well go 6 more to get a better planet. We don't yet know the atmosphere of Gliese 832 c, but, as Wikipedia notes,
However, because of its large mass, it may have a dense atmosphere, which could make it much hotter and more like the planet Venus, greatly reducing the chance for life. But you can check this out to listen to (well, read) an argument for why Gliese 832 c is a good choice. But it does admit the drawbacks of the planet.
And we're going to have to figure that out before we leave. If we can't - well, scratch that off the list. I doubt anyone's going to want to take that chance. It would be like going on a vacation to the Caribbean (not my personal choice, but others like it) and finding that global warming has raised sea levels so much that most of the islands are gone. Ouch.
That evaluation is really just for those two planets, though. Like I mentioned at the beginning, there are a lot more factors we have to take into account right here at home.
- How urgent are we? If ya gotta go, ya gotta go. If we're in a wee bit of a rush, we can leave the planet. There's no doubt about it. The thing is, at the moment, we'd be hard pressed to get more than ten people off the Earth within a few days. Yep. That's bad. But if we knew in advance what the issue was that was forcing us to leave, then we could plan ahead. (Not that I'm advocating getting rid of one-third of the population of Earth.) But the point is, if we can plan ahead, we can make a choice. If we have, say, a month before a huge asteroid hits and destroys a fair portion of the planet, we'll be able to get some people off. If we have a year or two, then we can decide.
- Who are we sending? IF we're sending a few explorers to go over and say "Hi" to any intelligent forms of life out there, or just to collect a couple of space rocks (I know, very unrealistic), the we might not worry about the planet's condition. After all, we'll be sending in some tough men and women. They can cope with anything. But if we're sending everyone, we have to make sure that they'll all be able to survive. It's not like we can just chuck the old folks into space. That's inhumane.
- How long are we staying there for? If we're staying there forever, then we need to make a choice that will determine the future of our race. We would, then, pick the one that is best suited for life (well, duh!). This means that we're probably willing to sacrifice some time in order to get a better planet. After all, we might not leave it.
Now we get to the meat of the question. I know that this is what you were most (by far) interested in, but I ignored it. Why? Well, we might actually be okay with the planets as they are. You saw the list of upsides and downsides. Stable star, decent masses, etc. We can't change the orbits easily, that's for sure. We can't change the distance from the star or the orbital eccentricity. But we might not need to. Sure, colonizing one of these wouldn't be easy. But we might not need to terraform them. High ESI, as you mentioned. Although I'm a bit wary of that, because there are a lot of factors that determine a planet's habitability.
But if the planets aren't so nice, and we really have to go to one. . . Again, it depends on urgency. Will we be able to bring enough stuff to terraform? I would hope so. If you can terraform one, you can bring enough equipment to terraform the other. They're pretty similar. But the big thing is, terraforming is hard. Really, really, hard. Don't just read the section in that link on Ethics; keep reading. The only reason Mars is on the table for terraforming is that we can get there within a year, under the best circumstances. I don't know if there's a point to going out 16 or 22 light-years, bringing all the supplies just to survive, and somehow being able to terraform a planet. It's not going to happen. And to be honest, the distance to the planets shouldn't impact our decision to terraform. It's not like we've got milk that's going to spoil if we go a little further. The only factor is if we're willing to wait. And if we're willing to wait for the time it takes to travel 16 light-years, we'll be willing to wait a little more.
My whole point is that we should really just settle on one of the planets. I spend a long time just listing out their pros and cons, and I did that to try to convince you that we don't need to terraform them. They're good just as they are. They've got enough Earth-like factors (and a high enough ESI, if that convinces you) that they could be very friendly to life. If there isn't some there already.