I have a Focus, it has a gotten a best of 32mpg on the highway. I'm not too enthusiastic about Ecomodding it, the ZX2 started out way better than that. However the Focus is a nicer car. It all depends on your priorities. The ZX2 MTX swap is the cheapest route, if you got a swap car, then you might as well put the whole motor and trans into yours. With the Focus, you get a nicer car with a strong aftermarket, but it has plenty of it's own problems, I'd say it has more issues than the ZX2! The ZX2 really only has a few issues, and they are easily resolved.
You know I'm a ZX2 enthusist though, so I'm biased
Good luck on your decision Zach!